May 28, 2021

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"Off the grid" with the Zebra Danio...

As a kid, I think one of the most memorable sights in my first aquarium, complete with blue gravel and plastic plants, was my group of 8 Zebra Danios  (Danio rerio) racing at high speed around the tank in a furious fashion, as if they had to get somewhere in a big freaking hurry...only to reverse course, and do it all again. I've never forgotten how much I liked the Zebras- or almost every other Danio species kept in the aquarium. 

Yeah, this fish has been known to science- and the aquairum hobby- for a very long time.  It was first described by Francis Hamilton, a surgeon with the British East India Company, stationed  in West Bengal in the early 19th Century. He published "An Account of the Fishes Found in the River Ganges and its Branches" in 1822, in which he described this fish and 9 other Danio species.

The more I researched this fish beyond the usual aquarium hobby stuff, the more remarkable stuff I found. Like, there are no less than 13 scientifically recognized wild strains of this fish!

Interesting, huh?

And there's more cool stuff you can find in the scientific literature:

For example, ichthyologists feel that this fish, "...appears to be primarily an annual species in the wild, the spawning season starting just before the onset of the monsoon.."  And, "Spawning is induced by temperature and commences at the onset of the monsoon season. Food availability also acts as cue for breeding." (Source - Fishbase)

And about this "annual" thing. Sure, in the aquairum, they can live 4-5 years. However, in the wild, length- frequency analysis by researchers demonstrated two distinct "age classes"  during the summer months, 0 to one year, and 1 year...indicating that the main period of rapid growth in these guys takes place during the monsoon months (June-September), a period of high temperatures (up to 34 °C) and food availability.  Spinal curvature- a sign of old age in captive fishes, was not found in wild-caught specimens, leading researchers that the fishes expire well before this malady can occur.

SImple, boring, "beginner's fish" my ASS! The Zebra Danio is is increasingly being used by researchers as a model for studying genetic effects in vertebrate development. Zebra Danios are able to regenerate their heart, nervous tissues, retina, hearing tissues, and fins!

This fish has got a lot going on!

And the amazing thing about this fish is that it's probably THE most bulletproof species you can keep. In fact, I recall reading somewhere that it's "tolerated temperature range" based on wild type localities is from 76.2 – 101.5°F (24.6 – 38.6°C). I mean, if THAT isn't a broad range, nothing is! And it tolerates water with a pH from 6.0-8.0.

Yeah, these guys are hardly what you'd call "fussy" fish!

Its diet, based on gut content analysis, consists primarily of zooplankton and insects. The usual stuff, right? Well, it also revealed that the fishes consume filamentous algae, terrestrial insects (including small spiders) detritus, sand, and mud! No wonder this fish is considered literally eats anything! It feeds at the surface and in the substrate.

And you know me- once I hear that kind of stuff, I get these weird ideas like, "What if we mimic the conditions of the natural habitat of the fish? Would they do better? IS there an advantage somewhere?"

I think like this for so many fishes, as if to shun the fact that 90% of what we keep in the aquarium these days has never seen a stream, pond, or river...😆

It's just..I don't know..irresistible to me to think about this kind of stuff! Taking the most common of common aquarium fishes and giving them "throwback" conditions; seeing if it somehow "awakens" something locked into their genetic code over eons...something...

I mean, it's kind of silly, I suppose...there are so many other things to do in the hobby...yet I can't help but wonder if we can learn something from replicating some aspects of their long-forgotten wild habitats...

And, in regards to the Zebra Danio, what's interesting to me is the habitats in which these fish are found. One of the habitats is known as a "beel", which, according to Wikipedia, is "...a lake-like wetland with static water (as opposed to moving water in rivers and canals.)"

In one study of the locations in which these were found, out of 26 reported occurrences, 14 were in ponds, 3 were in ditches connected to rice paddies, or in the rice paddies themselves, and 9 were canals or small rivulets adjacent to larger rivers.

Typically, these fishes are found in Northern India, and this area is subjected to seasonal rainfall between the months of June and September due to the summer Monsoon, and the water levels and characteristics vary considerably at different times of the year. They are often found in inundated rice paddies and marginal pools/ditches adjacent to them, with silty, kind of turbid water with very little movement. During the dry times of the year, they spend their time in calm, shaded areas of streams, with rocky or gravel-strewn substrates. 

This is interesting, because it reminds me a bit of the Amazon igarape, although instead of rain forest, you've got rice paddies...

An excerpt from a paper I found online about this species describes the unique habitats in which they are found:

"(The Zebra Danio) appears to be a floodplain rather than a true riverine species.They are most commonly encountered in shallow ponds and standing water bodies, often connected to rice cultivation. This association with rice cultivation may relate to the use of fertilisers which may promote the growth of zooplankton, a major component of the zebrafish diet (Spence et al.) Spence et al. (2006) found no zebrafish either in rivers or temporary creeks that opened during the monsoon season.

Where zebrafish are found in streams and rivers, these typically have a low flow regime and zebrafish tend to be found at the margins (McClure et al. 2006). Observations of their vertical distribution indicated that they occupy the whole of the water column and occur as frequently in open water as amongst aquatic vegetation (Spence et al. 2006a)."

So, yeah, this whole "fast-moving stream" idea we in the hobby have about these fishes seems far less common than good old-fashioned rice paddies and shallow, more still bodies of water! The Zebra seems to inhabit a world of marginal plants, turbidity, silty substrates, and lots of food.

And, I've been playing with rice seeds, silted substrates, and turbid water lately! Hmmm...

So, my simple thought is...this fish seems to hang out in what we as hobbyists would think of us "less desirable" conditions for much of the year- the silty rice paddies and their adjacent ditches...And only spends the dry season in the more permanent, less turbid streams. Why would this be? Is there some advantage? Like food, better substrates for breeding, protection? Why the turbid water? What does it bring to the fishes?

Would there be an advantage to keeping a fish like the Zebra in different conditions different times of the year, as in nature? Or simply in a tank representing one of the two habitats it's found in. Would you WANT or NEED to? I mean, the fish has been a captive-bred staple of the hobby for almost a century...but I can't help but wonder why these fishes live the way they do in the wild. What advantages do these habitats hold for the fish?

Would you get different behaviors, colors, health, spawning out of the fish by doing this "seasonal transition"..? Using a very fine sand substrate, maybe mixed in with some mud or something similar to replicate the rice paddies, with pump returns very gently angled at the bottom to simulate turbidity?


This just might have been the most ever discussed in a hobby context about the obscure habitats and characteristics of one of the most pervasive fishes in the aquarium hobby. 

Again, why, you ask?

My answer? I just think it could be kind of cool. Weird, but cool.

Am I the only one who imagines weird stuff like this? Maybe?

On second thought- don't answer that!

I know, the fish is bred by the billion in fish farms all over the world, as are many much sexier, domesticated strains of its relatives...but wouldn't it be interesting to see what happens when you "repatriate" these "common" fishes to an uncommon execution of their natural habitats? 

I think it would be. In fact, I'm certain that it would be! It's a fave hobby tangent of mine. I think that we'll do a periodic series, where we look at the wild habitats of the hobby's most common fishes..."Off The Grid." 

Yes, the whole purpose of this piece is to encourage you to go "off the grid" with common fishes. Research them not in the hobby literature, and delve into some scholarly research about them instead. The insights you gather may not always be remarkable, but you might uncover just enough about the so-called "common fish" swimming at the LFS that you just might want to tackle them with a whole new approach!

Yes, your friends will think that your nuts. But that's the fun part of this, right?


What fish will YOU go "off the grid" with?

Stay curious. Stay resourceful. Stay brave. Stay educated...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

The Botanical-Style Aquarium: A "filter" of its own, and other biological musings...

A big thought about our botanical-style aquariums:

The aquarium-or, more specifically- the botanical materials which comprise the botanical-style aquarium "infrastructure" acts as a biological "filter system."

In other words, the botanical materials present in our systems provide enormous surface area upon which beneficial bacterial biofilms and fungal growths can colonize. These life forms utilize the organic compounds present in the water as a nutritional source.

Oh, the part about the biofilms and fungal growths sounds familiar, doesn't it?

Let's talk about our buddies, the biofilms, just a bit more. One more time. Because nothing seems as contrary to many hobbyists than to sing the praises of these gooey-looking strands of bacterial goodness!

Structurally, biofilms are surprisingly strong structures, which offer their colonial members "on-board" nutritional sources, exchange of metabolites, protection, and cellular communication. They form extremely rapidly on just about any hard surface that is submerged in water.

When I see aquarium work in which biofilms are considered a "nuisance", and suggestions that it can be eliminated by "reducing nutrients" in the aquarium, I usually cringe. Mainly, because no matter what you do, biofilms are ubiquitous, and always present in our aquariums. We may not see the famous long, stringy "snot" of our nightmares, but the reality is that they're present in our tanks regardless.

The other reality is that biofilms are something that we as aquarists typically fear because of the way they look. In and of themselves, biofilms are not harmful to our fishes. They function not only as a means to sequester and process nutrients ( a "filter" of sorts?), they also represent a beneficial food source for fishes.

Now, look, I can see rare scenarios where massive amounts of biofilms (relative to the water volume of the aquarium) can consume significant quantities of oxygen and be problematic for the fishes which reside in your tank. These explosions in biofilm growth are usually the result of adding too much botanical material too quickly to the aquarium. They're excaserbated by insufficient oxygenation/circulation within the aquarium.

These are very unusual circumstances, resulting from a combination of missteps by the aquarist.

Typically, however, biofilms are far more beneficial that they are reven emotely detrimental to our aquariums.

Nutrients in the water column, even when in low concentrations, are delivered to the biofilm through the complex system of water channels, where they are adsorbed into the biofilm matrix, where they become available to the individual cells.  Some biologists feel that this efficient method of gathering energy might be a major evolutionary advantage for biofilms which live in particularly in turbulent ecosystems, like streams, (or aquariums, right?) with significant flow, where nutrient concentrations are typically lower and quite widely dispersed.

Biofilms have been used successfully in water/wastewater treatment for well over 100 years! In such filtration systems the filter medium (typically, sand) offers a tremendous amount of surface area for the microbes to attach to, and to feed upon the organic material in the water being treated. The formation of biofilms upon the "media" consume the undesirable organics in the water, effectively "filtering" it!

Biofilm acts as an adsorbent layer, in which organic materials and other nutrients are concentrated from the water column. As you might suspect, higher nutrient concentrations tend to produce biofilms that are thicker and denser than those grown in low nutrient concentrations.

Those biofilms which grow in higher flow environments, like streams, rivers, or areas exposed to wave action, tend to be denser in their morphology. These biofilms tend to form long, stringy filaments or "streamers",which point in the direction of the flow. These biofilms are characterized by characteristic known as  "viscoelasticity." This means that they are flexible, and stretch out significantly in higher flow rate environments, and contract once again when the velocity of the flow is reduced.

Okay, that's probably way more than you want to know about the physiology of biofilms! Regardless, it's important for us as botanical-style aquarists to have at least a rudimentary understanding of these often misunderstood, incredibly useful, and entirely under-appreciated life forms.

And the whole idea of facilitating a microbiome in our aquariums is predicated upon supplying a quantity of botanical materials- specifically, leaf litter, for the beneficial organisms to colonize and begin the decomposition process. An interesting study I found by Mehering, et. al (2014) on the nutrient sequestration caused by leaf litter yielded this interesting little passage:

"During leaf litter decomposition, microbial biomass and accumulated inorganic materials immobilize and retain nutrients, and therefore, both biotic and abiotic drivers may influence detrital nutrient content."

The study determined that leaves such as oak "immobilized" nitrogen. Generally thinking, it is thought that leaf litter acts as a "sink" for nutrients over time in aquatic ecosystems.

Oh, and one more thing about leaves and their resulting detritus in tropical streams: Ecologists strongly believe that microbial colonized detritus is a more palatable and nutritious food source for detritivores than uncolonized dead leaves. The microbial growth which occurs on the leaves and their resulting detritus increases the nutritional quality of leaf detritus, because the microbial biomass on the leaves is more digestible than the leaves themselves (because of lignin, etc.).

Okay, great. I've just talked about decomposing leaves and stuff for like the 11,000th time in "The Tint"; so...where does this leave us, in terms of how we want to run our aquariums?

Let's summarize:

1) Add a significant amount of leaf litter, twigs, and botanicals to your aquarium as part of the substrate.

2) Allow biofilms and fungal growths to proliferate.

3) Feed your fishes well. It's actually "feeding the aquarium!"

4) Don't go crazy siphoning out every bit of detritus.

Let's look at each of these points in a bit more detail.

First, make liberal use of leaf litter in your aquarium. I'd build up a layer anywhere from 1"-4" of leaves. Yeah, I know- that's a lot of leaves. Initially, you'll have a big old layer of leaves, recruiting biofilms and fungal growths on their surfaces. Ultimately, it will decompose, creating a sort of "mulch" on the bottom of your aquarium, rich in detritus, providing an excellent place for your fishes to forage among. 

Allow a fair amount of indirect circulation over the top of your leaf litter bed. This will ensure oxygenation, and allow the organisms within the litter bed to receive an influx of water (and thus, the dissolved organics they utilize). Sure, some of the leaves might blow around from time to time- just like what happens in Nature. It's no big deal- really!

The idea of allowing biofilms and fungal growths to colonize your leaves and botanicals, and to proliferate upon them simply needs to be accepted as fundamental to botanical-style aquarium keeping. These organisms, which comprise the biome of our aquariums, are the most important "components" of the ecosystems which our aquariums are.

I'd be remiss if I didn't at least touch on the idea of feeding your aquarium. Think about it: When you feed your fishes, you are effectively feeding all of the other life forms which comprise this microbiome. You're "feeding the aquarium." When fishes consume and eliminate the food, they're releasing not only dissolved organic wastes, but fecal materials, which are likely not fully digested. The nutritional value of partially digested food cannot be understated. Many of the organisms which live within the botanical bed and the resulting detritus will assimilate them.

Now, we could go on and on about this topic; there is SO much to discuss. However, let's just agree that feeding our fishes is another critical activity which provides not only for our fishes' well-being, but for the other life forms which create the ecology of the aquarium.

And, let's be clear about another thing: Detritus, the nemesis of many aquarists- is NOT our enemy. We've talked about this for several years now, and I cannot stress it enough: To remove every bit of detritus in our tanks is to deprive someone, somewhere along the food chain in our tanks, their nutritional source. And when you do that, imbalances occur...You know, the kinds which cause "nuisance algae" and those "anomalous tank crashes."

The definition of this stuff, as accepted in the aquarium hobby, is kind of sketchy in this regard; not flattering at the very least:

"detritus is dead particulate organic matter. It typically includes the bodies or fragments of dead organisms, as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose or remineralize the material."

Shit, that's just bad branding.

The reality is that this not a "bad" thing. Detritus, like biofilms and fungi, is flat-out misunderstood in the hobby.

Could there be some "upside" to this stuff? 

Of course there is. 

I mean, even in the above the definition, there is the part about being "colonized by communities of microorganisms which act to decompose or remineralize..."

It's being processed. Utilized. What do these microorganisms do? They eat it...They render it inert. And in the process, they contribute to the biological diversity and arguably even the stability of the system. Some of them are utilized as food by other creatures. Important in a closed system, I should think.

This is really important. It's part of the biological operating system of our botanical-style aquariums. I cannot stress this enough. 

Now, I realize that the idea of embracing this stuff- and allowing it to accumulate, or even be present in your system- goes against virtually everything we've been indoctrinated to believe in about aquarium husbandry. Pretty much every article you see on this stuff is about its "dangers", and how to get it out of your tank. I'll say it again- I think we've been looking at detritus the wrong way for a very long time in the aquarium hobby, perceiving it as an "enemy" to be feared, as opposed to the "biological catalyst" it really is!

In essence, it's organically rich particulate material that provides sustenance, and indeed, life to many organisms which, in turn, directly benefit our aquariums.

We've pushed this narrative many times here, and I still think we need to encourage hobbyists to embrace it more.

Yeah, detritus.

Okay, I'll admit that detritus, as we see it, may not be the most attractive thing to look at in our tanks. I'll give you that. It literally looks like a pile of shit! However, what we're talking about allowing to accumulate isn't just fish poop and uneaten food. It's broken-down materials- the end product of biological processing.  And, yeah, a wide variety of organisms have become adapted to eat or utilize detritus.

There is, of course, a distinction.

One is the result of poor husbandry, and of course, is not something we'd want to accumulate in our aquariums. The other is a more nuanced definition. 

As we talk about so much around here- just because something looks a certain way doesn't mean that it alwaysa bad thing, right?

What does it mean? Take into consideration why we add botanicals to our tanks in the first place. Now, you don't have to have huge piles of the stuff littering your sandy substrate. However, you could have some accumulating here and there among the botanicals and leaves, where it may not offend your aesthetic senses, and still contribute to the overall aquatic ecosystem you've created.

If you're one of those hobbyists who allows your leaves and other botanicals to break down completely into the tank, what really happens? Do you see a decline in water quality in a well-maintained system? A noticeable uptick in nitrate or other signs? Does anyone ever do water tests to confirm the "detritus is dangerous" theory, or do we simply rely on what "they" say in the books and hobby forums?

Is there ever a situation, a place, or a circumstance where leaving the detritus "in play" is actually a benefit, as opposed to a problem?

I think so. Like, almost always.

Yes, I know, we're talking about a closed ecosystem here, which doesn't have all of the millions of minute inputs and exports and nuances that Nature does, but structurally and functionally, we have some of them at the highest levels (ie; water going in and coming out, food sources being added, stuff being exported, etc.).

There is so much more to this stuff than to simply buy in unflinchingly to overly-generalized statements like, "detritus is bad."

The following statement may hurt a few sensitive people. Consider it some "tough love" today: 

If you're not a complete incompetent at basic aquarium husbandry, you won't have any issues with detritus being present in your aquarium.


Don't overstock.

Don't overfeed.

Don't neglect regular water exchanges.

Don't fail to maintain your equipment.

Don't ignore what's happening in your tank.

This is truly not "rocket science." It's "Aquarium Keeping 101."

And it all comes full circle when we talk about "filtration" in our aquariums.

People often ask me, "What filter do you use use in a botanical-style aquarium?" My answer is usually that it just doesn't matter.  You can use any type of filter. The reality is that, if allowed to evolve and grow unfettered, the aquarium itself- all of it- becomes the "filter." 

You can embrace this philosophy regardless of the type of filter that you employ.

My sumps and integrated filter compartments in my A.I.O. tanks are essentially empty.

I may occasionally employ some activated carbon in small amounts, or throw some "Shade" sachets in there if I am feeling it- but that's it. The way I see it- these areas, in a botanical-style aquarium, simply provide more water volume, more gas exchange; a place for bacterial attachment (surface area), and perhaps an area for botanical debris to settle out. Maybe I'll remove them, if only to prevent them from slowing down the flow rate of my return pumps.

But that's it. 

A lot of people are initially surprised by this. However, when you look at it in the broader context of botanical style aquariums as miniature ecosystems, it all really makes sense, doesn't it? The work of these microorganisms and other life forms takes place throughout the aquarium.

I admit, there was a time when I was really fanatical about making sure every single bit of detritus and fish poop and all that stuff was out of my tanks. About undetectable nitrate. I was especially like that in my earlier days of reef keeping, when it was thought that cleanliness was the shit!

It wasn't until years into my reef keeping work, and especially in my coral propagation work, that I begin to understand the value of food, and the role the it plays in aquatic ecosystems as a whole. And that "food" means different things to different aquatic organisms. The idea of scrubbing and removing every single trace of what we saw as "bad stuff" from our grow-out raceways essentially deprived the corals and supporting organisms of an important natural food source.

We'd fanatically skim and remove everything, only to find out that...our corals didn't look all that good. We'd compensate by feeding more heavily, only to continue to remove any traces of dissolved organics from the water...

It was a constant struggle- the metaphorical "hamster wheel"- between keeping things "clinically clean" and feeding our animals. We were super proud of our spotless water. We had a big screen when you came into our facility showing the parameters in each raceway. Which begged the question: Were we interested in creating sterile water, or growing corals? 

Eventually, it got through my thick skull that aquariums- just like the wild habitats they represent-are not spotless environments, and that they depend on multiple inputs of food, to feed the biome at all levels. This meant that scrubbing the living shit (literally) out of our aquariums was denying the very biotia which comprised our aquariums their most basic needs.

That little "unlock" changed everything for me.

Suddenly, it all made sense. 

This has carried over into the botanical-style aquarium concept: It's a system that literally relies on the biological material present in the system to facilitate food production, nutrient assimilation, and reproduction of life forms at various trophic levels.

It's changed everything about how I look at aquarium management and the creation of functional closed aquatic ecosystems. 

It's really put the word "natural" back into the aquarium keeping parlance for me. The idea of creating a multi-tiered ecosystem, which provides a lot of the requirements needed to operate successfully with just a few basic maintenance practices, the passage of time, a lot of patience, and careful observation.

It means adopting a different outlook, accepting a different, yet very beautiful aesthetic. It's about listening to Nature instead of the asshole on Instagram with the flashy, gadget-driven tank. It's not always fun at first for some, and it initially seems like you're somehow doing things wrong.

It's about faith. Faith in Mother Nature, who's been doing this stuff for eons.

It's about nuance.

It's about looking at things a bit different that we've been "programmed" to do in the aquarium hobby for so long. It's about not being afraid to question the reasons why we do things a certain way in the hobby, and to seek ways to evolve and change practices for the benefits of our fishes. 

It takes time to grasp this stuff. However, as with so many things that we talk about here, it's not's simply an evolution in thinking about how we conceive, set up, and manage our aquariums. 


Sure, the aquairum is a "filter" of sorts, if you want to label it as such. However, it's so much more: A small, evolving ecosystem, relying on natural processes to bring it to life.

Wrap you head around that.

It might just change everything in the hobby for you.

Stay open-minded. Stay thoughtful. Stay bold. Stay curious. Stay diligent. Stay observant...

And Stay Wet.


Scott Fellman

Tannin Aquatics 





May 25, 2021


A slice of the bottom? Or a figment of our imagination?

I'm not much of an aquascaper, in the "classic" sense.

Like, you could give me a piece of wood and some rocks, and maybe I'll stumble onto something. However, I'll never be able to crank out those artistic, intricate aquascapes the you see on The 'Gram and elsewhere. Nope. Not me. What I tend to do is research wild habitats of my fishes, figure out what makes 'em tick, and then try to replicate the function and form of them in my tanks.

The results are often "unorthodox" in appearance.


Other times, they're a bit more interesting...

Occasionally, even rather attractive.

However, the result was achieved because I attempted to replicate what I saw in the natural habitat which I'm trying to represent. And usually, it's about the "details" I see in the habitat. Trying to recreate the details which fishes seem to be drawn to almost always results in something interesting- and attractive!

There is something enticing, stimulating, and challenging about recreating a literal slice of the bottom, isn't there? Asking yourself why these habitats form, what contributes to the way that they look, and how they support aquatic life forms unlocks a tremendous amount of information that you can use in your work.

Looking at wild aquatic habitats in this fashion provides tremendous inspiration, especially when you look at the "macro view" and isolate some of the details, like how wood falls, how  substrate and leaves accumulate, and where fishes seem to aggregate, in context.

Despite my "aesthetic challenges", I've always taken comfort in the fact that my wood arrangements almost always seem to look better once they're submerged and become part of a whole habitat. In fact, I don't think I've ever owned an aquarium where the wood scape looked "amazing" before it was submerged.

And that has never really bothered me. I don't get all hung up on creating the perfect "wood stack."

I'm far less into "aquascaping" in the traditional sense than I am in representing functional aspects of various natural habitats. And I think it's served me very well. As I've mentioned so often, the "look" of the botanical-style, natural aquarium always seems to come as a result of the function.

What typically happens is that the "lame" wood arrangement that I'll create recruits biofilms, softens up a bit over time. Perhaps, I'll gradually add a few pieces to it, and over time, it becomes something far more interesting and attractive than originally configured. 

However, the "editing" is based upon how the wild habitat that I'm trying to replicate evolves and functions. In many wild habitats, materials aggregate over time. This is interesting. It opens up the possibility of "evolving" your aquarium's appearance over time, as a result of replicating the function.

Have you thought much about how "clogged" with materials some of the natural habitats we intend to imitate in our tanks actually are?

More than you think.

It's kind of interesting to consider, and I've done a little "field work" over the years, as well as some "internet safaris", exploring some of the interesting habitats where our fishes come from, and I've frequently been surprised just how much "stuff" is in the water.

And of course, there is a strange "disconnect" with our hobby tinterpretation of Nature, and what is really out there.  It makes me think about our aquascapes, and how we are seemingly always concerned about having the "appropriate" amount of "negative space"- at least from an artistic perspective.

I mean, from an aquascaping point of view, I suppose that's quite understandable. And, I would imagine that there is a sort of a perception in the hobby that having an aquarium that's not densely-packed with materials is somehow more sustainable, healthier, etc. from a practical management standpoint.

Like, it's easier to maintain an aquarium that's more "open."

Or, is it?

Sure, you can easily get a siphon hose into a more open tank. You can keep detritus in suspension where it can be removed more easily-if that's your thing, of course.

You know my thoughts on "detritus..."

On the other hand, if you've made that "mental shift" to accepting a more natural-looking- and functioning aquarium, the amount of material you have in the tank makes little difference. You simply adjust your husbandry practices and stocking  to accommodate the physical "configuration" of the aquarium and go about your business!

Educating yourself about the realities of natural habitats, rather than strictly modeling our aquariums after other aquariums, can open you up to numerous examples of how these environments foster numerous life forms successfully.

When you take into account the materials that accumulate in smaller streams, igarapes, flooded meadows, and swamps- you know, the habitats we love around here- a surprisingly large amount of botanical materials, ranging from tree branches/trunks to leaves and such, accumulates and takes up a lot of physical space in the aquatic habitat.


Not only do these materials take up water volume and physical space- they serve to direct flow, create other hydrodynamic features, etc. More important, they also accumulate/sequester nutrients and food sources for the organisms which reside in these habitats.

In the aquarium, a larger volume of say, driftwood, rocks, and botanicals will not only impart the oft-mentioned "chemical" affects into the water, they will similarly channel flow, create territories, and offer areas of visual interest. Functional aesthetics.

Well-managed aquariums which are densely-packed with wood and botanical materials can create surprisingly dynamic, ever-evolving displays.


This is perfectly analogous to the seasonal evolutions of underwater landscapes in Nature, as waters recede after the rainy season, leaving a more densely-packed assemblage of materials in a given area.

To get a better perspective on this, look at the rain forest floor in tropical regions, such as Amazonia. After all, this is what is left during the dry season, and gives you some idea of the eventual "topography" of the underwater landscape when the rains return. 

Rain performs the dual function of diluting organics, while transporting more nutrient and materials across the ecosystem. What happens in many of the regions of Amazonia, for example- is the evolution of our most compelling environmental niches. The water levels in the rivers rise significantly. often several meters, and the once dry forest floor fills with water from the torrential rain and overflowing rivers and streams.

The Igapos are formed. 

Flooded forest floors. Yeah, I talk about this habitat incessantly. I'm obsessed by it.

The formerly terrestrial environment is now transformed into an earthy, twisted, incredibly rich aquatic habitat, which fishes have evolved over eons to live in and utilize for food, protection, and spawning areas.

It's not just the igapo that receive regular "deliveries" of terrestrial materials!

Many bodies of water which meander through jungles and rain forests are constantly being "restocked" with leaves, seed pods, branches, and other botanical materials from the surrounding vegetation- some of which are knocked into the water by weather, wind, animal activity, etc. Depending upon the velocity of the water, its depth, etc., they may aggregate right where they fall, or be gradually re-distributed downstream by the current.

I can't tell you how amazing this type of habitat is to replicate in the aquarium! It challenges our aesthetic tastes, our skills at managing closed systems, and our ability to understand the benefits of having all of this stuff present in our tanks.

Now, I'm not telling you that you should fill your tanks to the rim with wood, seed pods, leaves, and rocks (although it sounds like a cool idea, doesn't it? LOL). I AM suggesting that you look into the physical structure of these habitats, and consider interesting functionally aesthetic impacts that  you can create with a more "dense" scape. Attempt to understand the function and benefits to your fishes created by such a configuration. 


We've already touched on some of the benefits above; analogous to those found in the natural habitats they attempt to represent, and this is increasingly obvious to all of us who play with botanical-style aquariums.

Now, the one of the immediate "downsides" most hobbyists who are unfamiliar with our practices and philosophies on aquarium management will jump on is, "Hey, more 'stuff' in the water means...less water can't have as many fishes in your tank."Absolutely. Sure. On the other hand, lower population densities of fishes could actually serve to create a more visually engaging display!

Not only will there be functional and environmental benefits as a result of lower fish populations- you'll probably find some aesthetic ones, as well. And the ability to study "niche" fishes and their habitat preferences is pretty damn interesting, IMHO!

And a rather densely-packed tank isn't exactly a new concept in the aquarium hobby.

I remember back in the 1980's through the early 2000's, in the earlier days of the modern reef aquarium craze, we were obsessed with the concept of "live rock" as a "filter medium", and the prevailing wisdom was that you needed "x" amount of rock per given volume of water in a reef tank...

And it was quite a bit...Of course, the best way to achieve this "recommended quantity" was to create a literal "wall of rock", something that I have railed on personally for years in my writings and presentations.

It looked pretty crazy. However, it defined he aesthetics of the reef aquarium for a generation of hobbyists. And it did work, despite some limitations unique to the reef side of the hobby (ie; flow and ability to access, etc.)

So, yeah, I'd be a bit hypocritical if I was  suggesting a "wall of botanicals" and such; however, I think it would be interesting to play with higher densities of wood and botanicals in some displays. To encourage areas of interest. Yes, fascinating details which encourage the observer to really study the aquarium in a more focused way.

Nature offers the model:

In Nature, all of the botanical material- fallen leaves, branches, seed pods, and such create the biological "operating system" for the aquatic environment.  Soils dissolve their chemical constituents- tannins, and humic acids- into the water, enriching it. Fungi and micororganisms begin to multiply, feed on and break down the materials. Biofilms form, crustaceans reproduce rapidly.  Fishes are able to find new food sources; new hiding areas to spawn.

Life flourishes.

Fishes and other aquatic organisms are able to make use of all of the physical materials deposited into their environment.

It works.

Let's get back to the "practical" aspects again, vis a vis our aquairums.

There are some keys to maintaining aquarium filled with materials like decomposing leaves and botanicals. We know this by now; it's become part of our "best practices..." You definitely need to do regular maintenance. You don't want to overstock...I mean, common sense stuff. However, in a tank filled with considerable organic material, "slight overstocking" and poor general husbandry can be problematic. 

It's about husbandry and perspective...

And it's about accepting the fact that the leaves and other natural materials are part of the ecology of the tank, and that they will behave as terrestrial materials do when submerged:

They'll break down and decompose. They'll form the basis of a surpassingly complex food chain, which includes bacterial biofilms, fungi, and minute crustaceans. Each one of these life forms supporting, to some extent, those above...including our fishes.


When you think of the botanical materials not so much as "hardscape props", but as dynamic biological components of a closed microcosm, it all makes a bit more sense. And the more material that is present in the system, the greater the "fuel" available for microbial growth to "power" the system.

And when we add/remove/supplement more leaves and botanicals, and allow others to fully break down in our tanks, we are perfectly replicating the natural processes which occur in streams and rivers around the world. 

Think about the materials which accumulate in natural aquatic habitats, and how they actually end up in them, and it makes you think about this in a very different context. A more "holistic" context that can make your experience that much more rewarding. Botanicals should be viewed as "consumables" in our hobby- much like activated carbon, filter pads, etc.- they simply don't last indefinitely.

And the biofilms and algal growths which appear on our leaves and botanicals-just as they do in the wild habitats we mimic- provide not only a degree of "biological functionality" for our systems, but an evolving aesthetic as well.

Embrace these things- don't fear them.

Understand that the real "designer" of our botanical-style aquaecapes is Mother Nature herself.

We just set the stage.

So- set the stage, and enjoy the random, compelling, and ever-evolving work of art that is the blackwater/botanical-style aquarium. Started by you. Evolved with the steady hand of Nature.

Look, I adore minimalist stuff...abosolutely. However, I'd think it would be interesting (and entirely authentic to Nature) to play with a more complex, "heavy-handed" scape once in a while. Not just for their interesting aesthetics, mind you.


Where it gets really interesting is in a larger aquarium, with a population of smaller fishes dwelling in such a 'scape. For example, imagine the allure of a tank, heavily "choked" with thin wood branches, some larger seed pods, bark, and leaves.

By selecting smaller fishes like Tetras, Apsitos, Boraras, Guaramis, Badis, Corydoras, etc., you could maximize the impact by having a fairly high number of fishes in an aquascape that offers a lot less open area, encouraging the fishes to engage in more natural behaviors, like swimming through, and foraging among the dense wood and botanical areas.

If you stock with fishes like Elachocharax, for example- that are known to inhabit more densely packed areas of streams and such, or very specific areas like leaf litter zones, you can create a very unique and engaging display in which the fishes won't be immediately evident to the observer.

As with the "jungle" planted tanks I adore so much, the densely stocked botanical-style aquarium encourages the observer to take the time to "linger" and "discover" the fishes flitting in and out of the hardscape...

Like in any botanical aquarium, a more densely-packed one will require thoughtful, but not excessive maintenance. You'll simply need to feed carefully, stock thoughtfully, and adhere to the typical tenants of aquarium keeping. There is very little that is actually more difficult to manage about this type of tank than any other, when you understand its dynamics.

And a more densely packed one will find its way, like any other natural, botanical-style aquarium, developing over time into an intriguing, engaging display that will become a constantly-evolving, highly engaging, and oddly refreshing aquarium.

The appeal of this interesting aesthetic, and the practical benefits may or may not be immediately obvious to you. However, I encourage you to consider an aquatic habitat such as this as a subject for your next project.

The good news is that, if you find that you aesthetically prefer a more "open" scape, you can simply remove wood, botanicals, etc., until you hit the aesthetic that appeals to you.

And even that, in itself is not unlike the natural processes of current, tidal movements, etc. which "re-arrange" the natural ecosystems all the time!

In the end, turning once again to the incredible, almost infinite "portfolio" of inspiration which Nature provides seems to always provide will steer you in the right direction. If you look at enough natural aquatic systems, you'll no doubt be struck by some habitat that speaks to you, motivates you to replicate it in some way...and to share your work with others.

With the precious natural environments subject to so many dangerous external forces and perils, perhaps one of the most significant steps we can take to help preserve them is to help others appreciate them by modeling an aquarium after them.

And that may mean embracing more unorthodox aesthetics.

Look at, and consider exactly what it is that makes these wild habitats so successful. You will likely find that so much of what makes these ecosystems operate so successfully starts with the bottom!

Yeah, that means the substrate, and the accompanying "topography" of the benthic habitat.

Stream and river bottom composition is affected by things like regional weather, current, geology, the surrounding dry lands, and a host of other factors- all of which could make planning your next aquarium even more interesting if you take them into consideration!

We've touched on these in some recent posts, and we'll definitely dive deeper in upcoming blogs. There's more to this habitat than just the accumulation of leaves and such.

It's pretty interesting...

If we focus on shallow tributaries of streams and flooded forest floors, it's important to note that the volume of water entering the stream helps, in part, to determine the amount and size of sediment particles, leaves, beaches, seed pods, and the like that can be carried along, and thus comprise the substrate and it's contours.

The mixing of materials not only looks interesting- it's a reflection of the diversity and vibrancy of the underwater environment.

One of the things you notice in the images above of natural underwater substrates is that they're usually anything but squeaky-clean, ultra-white sand. Rather, they're often sediment-filled, covered with stringy fungal growths, biofilms, and even a spot or two of algae. There is a fair amount of detritus accumulating in the substrate materials. And, as you know, detritus is not the enemy that we've made it out to be. Rather, it's a source of food for many aquatic animals, helping to literally "power" the ecosystem in which they are present.

This is something we can-and should- absolutely replicate in our aquariums. Don't be afraid of sediments and even detritus accumulating on top of your leaves and's exactly what you see in Nature, and our fishes are ecologically adapted to such habitats.

In Nature, the composition of bottom materials and the depth of the channel are always changing in response to the flow in a given stream, affecting the composition and ecology in many ways. Some of these changes are actually the result of the fishes "working them."

 In the words of our friend, author Mike Tuccinardi:

"One of the things that is most striking when you spend time below the water’s surface in this sort of environment is that the fish aren’t just passive inhabitants—they’re actively involved with their habitat, interacting in a very particular way. Apistogramma species aren’t just hanging out, they’re fighting turf wars among piles of dense leaf litter, even making their own piles by moving leaves and other bits of detritus to the center of their territories.

Suckermouth catfish, whether Farlowella or Ancistrus, are actively exploring recently-submerged branches and roots, looking for a rich patch of biofilm or algae to feast on. Eartheaters and many other species of cichlids—even Severums, Angelfish, and Discus—are patrolling the bottom, taking big mouthfuls of sand and organic material to sift out any tasty morsels. It’s a big, organic mess, literally made up of various botanicals and these fish are having a field day in it."

These dynamic habitats are not difficult to replicate in the aquarium. We need to understand that they play a functional and aesthetic role in the overall aquarium, as we've touched on many times here. Realizing that placing leaves and botanical materials on the bottom of the aquarium is not simply making an aesthetic statement.

Rather, it's an homage to the function of the dynamic habitats we love so much. Yet, there is plenty of room for creativity, of course.

The natural beauty of recreating these "slices of the bottom" in our aquariums, embracing function over simple aesthetics, may just motivate aquarists and non-aquarists alike to take a greater interest in helping preserve and protect these precious natural ecosystems.

And that's the biggest "win" of all! 

Remember, replicating natural aquatic habitats in form and function is really not a "style" or trend in the aquarium world.

Nature isn't exactly a "fad" or trend-follower, right? She's been doing this stuff for eons. We're just sort of "catching up"- and beginning to study, contemplate, and appreciate what happens when form meets function in the aquarium.

It just happens to look kind of cool.

And that's pretty exciting, isn't it?

I think that it is.

Stay engaged. Stay curious. Stay dedicated. Stay observant. Stay open-minded...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Botanical materials in the wild...and in the aquarium: Influences and Impacts.

As you know, we've spent the better part of the past 6 years talking about every aspect of the botanical-style aquarium that we can think of. We've talked about techniques, approaches, ideas, etc. And we've spent a lot of time sharing information about wild aquatic habitats that we might be interested in replicating in both form and function.

However, I think we haven't spent as much time as we should talking about how botanicals "behave" in wild aquatic habitats.  Much of this stuff has implications for those of us who are interested in replicating these habitats in our aquariums. So, let's dive in a bit more on this topic today!

Among the trees of the flooded forests, after the fruits mature (which occurs at high water levels), seeds will fall into the water and may float on the surface or be submerged for a number of weeks. Ecologists believe that the seed production of the trees coincides with the flood pulses, which facilitates their dispersal by water movement, and by the actions of fish.

Interestingly, scientists postulate that these floating or sinking seeds, which  germinate and establish seedlings after the flood waters recede, do very well, sprouting and establishing themselves quickly, and are not severely affected by waterlogging in most species.

So, within their cycle of life, the trees take advantage of the water as part of their ecological adaptation. Trees in these areas have developed specialized morphologies, such as advantageous roots, butress systems and stilt roots.

 In a lot of wild aquatic habitats where leaf litter and other allochthonous materials accumulate, there are a number of factors which control the density, size, and type of materials which are deposited in streams and such. The flow rate of the water within these habitats determines a lot of things, such as the size of the leaves and other botanical materials  and where in the stream they are deposited. 

I often wonder how much the fallen leaves and seed pods impact the water chemistry in a given stream, pond, or section of an Amazonian flooded forest. I know that studies have been done in which ecologists have measured dissolved oxygen and conductivity, as well as pH. However, those readings only give us so much information.

We hear a lot of discussion about blackwater habitats among hobbyists, and the implications for our aquariums. And part of the game here is understanding what it is that makes this a blackwater river system to begin with. We often hear that blackwater is "low in nutrients." 

What exactly does this mean?

One study concluded that the Rio Negro is a blackwater river in large part because the very low nutrient concentrations of the soils that drain into it have arisen as a result of "several cycles of weathering, erosion, and sedimentation." In other words, there's not a whole lot of minerals and nutrients left in the soils to dissolve into the water to any meaningful extent!

Black-waters, drain from older rocks in areas like the Negro river, result from dissolved fulvic and humic substances, present small amounts of suspended sediment, lower pH (4.0 to 6.0) and dissolved elements. Yes, highly leached tropical environments where most of the soluble elements are quickly removed by heavy rainfall.

Perhaps...another reason (besides the previously cited limitation of light penetration) why aquatic plants are rather scare in these waters? It would appear that the bulk of the nutrients found in these blackwaters are likely dissolved into the aquatic environment by decomposing botanical materials, such as leaves, branches, etc.

Why does that sound familiar?

Besides the color, of course, the defining characteristics of blackwater rivers are pH values in the range of 4-5, low electrical conductivity, and minimal mineral content. Dissolved minerals, such as  Ca, Mg, K, and Na are negligible. And with these low amounts of dissolved minerals come unique challenges for the animals who reside in these systems.

How do fishes survive and thrive in these rather extreme habitats?

It's long been known that fishes are well adapted to their natural habitats, particularly the more extreme ones. And this was borne out in a recent study of the Cardinal Tetra. Lab results suggest that humic substances  protect cardinal tetras in the soft, acidic water in which they resides by preventing excessive sodium loss and stimulating calcium uptake to ensure proper homeostasis.

This is pretty extraordinary, as the humic substances found in the water actually enable the fishes to survive in this highly acidic water which is devoid of much mineral content typically needed for fishes to survive!

And of course, botanicals, leaves, and wood typically have an abundance of these humic substances, right? They are useful for more than just an interesting and unique aesthetic effect! There is a lot of room for research about influencing the overall environment in our aquariums here! I think we've barely scratched the surface of the potential for utilizing botanicals in our aquariums.

This is another one of those foundational aspects of the natural style of aquarium that we espouse. The understanding that processes like decomposition and physical transformation of the materials that we utilize our tanks are normal, expected, and beautiful things requires us to make mental shifts.

Botanical materials don't have nearly as much impact on the water parameters (other than say, conductivity and dissolved oxygen) as the soils do. These waters have high concentrations of humic and fulvic acids derived from sandy "hydromorphic podsols" prevalent in the region.  However, these allochthonous materials have huge impact on the ecology of these systems!

Leaf litter, as one might suspect, is of huge importance in these ecosystems. Especially in smaller tributaries. In one study which I came across, it was concluded that, "The smaller the stream, the more dependent the biota is on leaf litter habitats and allocthonous energy derived directly or indirectly from the forest." (Kemenes and Forsberg)

From the same study, it was concluded that the substrate of the aquatic habitat had significant influence on the feeding habits of the fishes which resided in them: 

"The biomass of allocthonous insectivore increased in channels with a higher percentage of sandy bottom substrate. Detritivorous insectivore biomass, in contrast, increased significantly in channels with a higher percentage of leaf substrate. General insectivores tended to increase in streams with higher proportions of leafy substrate, too.

Whats the implication for us as hobbyists? Well, for one thing, we can set up the benthic environment in our tanks to represent the appropriate environment for the fishes which we want to keep in them. Simple as that!

t's as much about function as anything else. And, about pushing into some new directions. The unorthodox aesthetics of these unusual aquariums we play with just happen to be an interesting "by-product" of theirfunction.

I personally think that almost every botanical-style aquarium can benefit from the presence of leaves. As we've discussed numerous times, leaves are the "operating system" of many natural habitats (ecology-wise), and perform a similar role in the aquarium.

The presence of botanical materials such as leaves in these aquatic habitats is fundamental. Leaves and other botanicals are extremely pervasive in almost every type of aquatic habitat.

In the tropical species of trees, the leaf drop is important to the surrounding environment. The nutrients are typically bound up in the leaves, so a regular release of leaves by the trees helps replenish the minerals and nutrients which are typically depleted from eons of leaching into the surrounding forests.

Now, interestingly enough, most tropical forest trees are classified as "evergreens", and don't have a specific seasonal leaf drop like the "deciduous" trees than many of us are more familiar with do...Rather, they replace their leaves gradually throughout the year as the leaves age and subsequently fall off the trees.

The implication here?

There is a more-or-less continuous "supply" of leaves falling off into the jungles and waterways in these habitats, which is why you'll see leaves at varying stages of decomposition in tropical streams. It's also why leaf litter banks may be almost "permanent" structures within some of these bodies of water!

Our botanical-style aquariums are not "set-and-forget" systems, and require basic maintenance (water exchanges, regular water testing, filter media replacement/cleaning), like any other aquarium.  They do have one unique "requirement" as part of their ongoing maintenance which other types of aquariums seem to nothave: The "topping off" of botanicals as they break down.

The "topping off" of botanicals in your tank accomplishes a number of things: first, it creates a certain degree of environmental continuity- keeping things consistent from a "botanical capacity" standpoint. Over time, you have the opportunity to establish a "baseline" of water parameters, knowing how many of what to add to keep things more-or-less consistent, which could make the regular "topping off" of botanicals a bit more of a "science" in addition to an "art."

In addition, it keeps a consistent aesthetic "vibe" in your aquarium. Consistent, in that you can keep the sort of "look" you have, while making subtle- or even less-than-subtle "enhancements" as desired. 

Yeah, dynamic.

And, of course, "topping off" botanicals helps keeps you more intimately "in touch" with your aquarium, much in the same way a planted tank enthusiast would by trimming plants, or a reefer while making frags. When you're actively involved in the "operation" of your aquarium, you simply notice more. You can also learn more; appreciate the subtle, yet obvious changes which arise on an almost daily basis in our botanical-style aquariums.

I dare say that one of the things I enjoy doing most with my blackwater, botanical-style aquariums (besides just observing them, of course) is to "top off" the botanical supply from time to time. I feel that it not only gives me a sense of "actively participating" in the aquarium- it provides a sense that you're doing something nature has done for eons; something very "primal" and essential. Even the prep process is engaging.

Think about the materials which accumulate in natural aquatic habitats, and how they actually end up in them, and it makes you think about this in a very different context. A more "holistic" context that can make your experience that much more rewarding. Botanicals should be viewed as "consumables" in our hobby- much like activated carbon, filter pads, etc.- they simply don't last indefinitely.

Many seed pods and similar botanicals contain a substance known as lignin. Lignin is defined as a group of organic polymers which are essentially the structural materials which support the tissues of vascular plants. They are common in bark, wood, and yeah- seed pods, providing protection from rotting and structural rigidity.

In other words, they make seed pods kinda tough.

Yet, not permanent.

That being said, they are typically broken down by fungi and bacteria in aquatic environments. Inputs of terrestrial materials like leaf litter and seed pods into aquatic habitats can leach dissolved organic carbon (DOC), rich in lignin and cellulose. Factors like light intensity, mineral hardness, and the composition of the aforementioned bacterial /fungal community all affect the degree to which this material is broken down into its constituent parts in this environment.

Hmm...something we've kind of known for a while, right?

So, lignin is a major component of the "stuff" that's leached into our aquatic environments, along with that other big "player"- tannin.

Tannins, according to chemists, are a group of "astringent biomolecules" that bind to and precipitate proteins and other organic compounds. They're in almost every plant around, and are thought to play a role in protecting the plants from predation and potentially aid in their growth. As you might imagine, they are super-abundant in...leaves. In fact, it's thought that tannins comprise as much as 50% of the dry weight of leaves!


And of course, tannins in leaves, wood, soils, and plant materials tend to be highly water soluble, creating our beloved blackwater as they decompose. As the tannins leach into the water, they create that transparent, yet darkly-stained water we love so much!  

In simplified terms, blackwater tends to occur when the rate of "carbon fixation" (photosynthesis) and its partial decay to soluble organic acids exceeds its rate of complete decay to carbon dioxide (oxidation).

Chew on that for a bit...Try to really wrap your head around it...

And sometimes, the research you do on these topics can unlock some interesting tangential information which can be applied to our work in aquairums...

Interesting tidbit of information from science: For those of you weirdos who like using wood, leaves and such in your aquariums, but hate the brown water (yeah, there are a few of you)- you can add baking soda to the water that you soak your wood and such in to accelerate the leaching process, as more alkaline solutions tend to draw out tannic acid from wood than pH neutral or acidic water does. Or you can simply keep using your 8.4 pH tap water! 

"ARMCHAIR SPECULATION": This might be a good answer to why some people can't get the super dark tint they want for the long term...If you have more alkaline water, those tannins are more quickly pulled out. So you might get an initial burst, but the color won't last all that long...

I think just having a bit more than a superficial understanding of the way botanicals and other materials interact with the aquatic environment, and how we can embrace and replicate these systems in our own aquariums is really important to the hobby. The real message here is to not be afraid of learning about seemingly complex chemical and biological nuances of blackwater systems, and to apply some of this knowledge to our aquatic practice.

It can seem a bit  intimidating at first, perhaps even a bit contrarian to "conventional aquarium practice", but if you force yourself beyond just the basic hobby-oriented material out there on these topics (hint once again: There aren't many!), there is literally a whole world of stuff you can learn about!

It starts by simply looking at Nature as an overall inspiration...

Wondering why the aquatic habitats we're looking at appear the way they do, and what processes create them. And rather than editing out the "undesirable" (by mainstream aquarium hobby standards) elements, we embrace as many of the elements as possible, try to figure out what benefits they bring, and how we can recreate them functionally in our closed aquarium systems.

There are no "flaws" in Nature's work, because Nature doesn't seek to satisfy observers. It seeks to evolve and change and grow. It looks the way it does because it's the sum total of the processes which occur to foster life and evolution.

We as hobbyists need to evolve and change and grow, ourselves.

We need to let go of our long-held beliefs about what truly is considered "beautiful." We need to study and understand the elegant way Nature does things- and just why natural aquatic habitats look the way they do.  To look at things in context.  To understand what kinds of outside influences, pressures, and threats these habitats face.

And, when we attempt replicate these functions in our aquariums, we're helping to grow this unique segment of the aquarium hobby.

Please make that effort to continue to educate yourself and get really smart about this stuff...And share what you learn on your journey- all of it- the good and the occasional bad. It helps grow the hobby, foster a viable movement, and helps your fellow hobbyists!

Stay studious. Stay thoughtful. Stay inquisitive. Stay creative. Stay engaged...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


May 21, 2021


Supplemental? Primary? Or both?

Among the many interesting ideas floating around in the botanical-style aquarium world is the idea that use of botanical materials can help provide supplemental (or primary, in some instances) food sources for our fishes. We have touched on this idea for years now, and the more we play with these aquariums, the more I'm convinced that yet another collateral benefit of them is food production.

It's hardly a stretch to propose this, right? I mean, just like in Nature, a typical botanical-style aquarium has an accumulation of organic materials, a healthy population of organisms to process them, and supports a large amount of life at many "trophic levels."

What is also studied by science, but a little more "esoteric" in the hobby (IMHO) is the use of botanical materials as supplemental food for our fishes and shrimps. 

Now, it's known that most plant materials have at least some nutritional value; or rather, they contain nutrients, vitamins, etc. which are known to be beneficial to aquatic organisms. Which ones are the best for use as "supplemental foods?"

Or, are they all pretty good? 


Well, here's the thing...

The thing that makes me curious is that most leaves and botanicals contain vitamins, amino acids, micronutrients, and other "bioavailable compounds." The real question I have is exactly how "available" they are to our fishes and shrimp from a nutritional standpoint. And how "nutrient dense" these leaves and botanicals are? Do our fishes and shrimp easily assimilate all they need in every bite, or do they have to eat tons of the stuff to derive any of nutritional benefits?

Big questions, right?

I mean, we as hobbyists sort of tend to make this (gulp) assumption that if these things are present in the botanicals, then our animals get a dose of them in every bite, right? And, it begs the question: Are they really directly consuming stuff like Casuarina cones, or feeding on something else on their surfaces (more on this later)?

I think it's "yes" on both.

And the nutrition that they derive from consuming them?

Well, that's the part where I say, I don't know for sure.

I mean, it seems to make a lot of sense to me...However, is there some definitive scientific information out there to prove this hypothesis?

A lot of the "botanicals for food thing" in the hobby (no, seriously- it's a "thing!") comes from the world of shrimp keepers. They've been touting this stuff in the hobby for a long time. A lot of it is based upon the presence of materials like leaves and such in the wild habitats where shrimp are found. I did some research online (that internet thing- I think it just might catch on...) and learned that in aquaculture of food shrimp, a tremendous variety of vegetables, fruits, etc. are utilized, and many offer good nutritional profiles for shrimp, in terms of protein, amino acids, etc.

They're all pretty good. Our friend Rachel O'Leary did a great job touching on the benefits of botanicals for shrimp in her video last Fall.

So, which one is the best? Is there one? Does it matter? In fact, other than sorting through mind-numbing numbers ( .08664, etc) on various amino acid concentrations in say, Mulberry leaves, versus say, Sugar Beets, or whatever, there are not huge differences making any one food superior to all others, at least from my very cursory, non-scientific hobby examination! 

Leaves like Guava, Mulberry, etc. ARE ravenously consumed directly by shrimp and some fishes. It's known by scientific analysis that they do contain compounds like Vitamins B1, B2, B6, and Vitamin C, as well as carbohydrates, fiber, amino acids, and elements such as Magnesium, Potassium, Zinc, Iron, and Calcium...all important for many organisms, including shrimp. Guava leaves are particularly good, according to some of the materials I read. Apparently, the bulk of the nutrients they contain are more "readily available" to animals than other leaves.

Well, that's pretty important, isn't it?

I think so!

Now, it may be coincidental that these much-loved (by the shrimp, anyways) leaves happen to have such a good amount of nutritional availability, but it certainly doesn't hurt, right?

Other leaves, such as Jackfruit, contain phytonutrients, such as lignins, isoflavones, and saponins that have health benefits that are wide ranging for humans. There is some conflicting data regarding Jackfruit's alleged antifungal properties. However, the leaves are thought to exhibit a broad spectrum of antibacterial activity. In traditional medicine, these leaves are used to help heal wounds as well.

In humans.

Do these properties transfer over to our fishes and shrimp?

Here's the straight answer: We are not aware of any scientific studies that have been completed to correlate one way or another. That being said, they seem to flock to these leaves and graze on them- and on the biofilms which accumulate on their surface tissues. 


The "shrimp side" of the hobby reminds me in some ways of the coral part of the reef keeping hobby where I spent considerable time (both personally and professionally) working and interacting with the community. There are some incredibly talented shrimp people out there; many doing amazing work and sharing their expertise and experience with the hobby, to everyone's benefit!

Now, there are also a lot of people out there in that world -vendors, specifically- who make some (and this is just my opinion...), well - "stretches"- about products and such, and what they can do and why they are supposedly great for shrimp. I see a lot of this in the "food" sector of that hobby specialty, where manufacturers of various foods extoll the virtues of different products and natural materials because they have certain nutritional attributes, such as vitamins and amino acids and such, valuable to human nutrition, which are also known to be beneficial to shrimp in some manner. 

I mean, do shrimp really derive benefits from stuff like nettles? Well, perhaps they contain micronutrients or other compounds which are known to be beneficial to organisms. And that's fine, but where it gets a bit anecdotal, or - let's call it like I see it- "sketchy"- is when read the descriptions about stuff like leaves and such on vendors' websites which cater to these animals making very broad and expansive claims about their benefits, based simply on the fact that shrimp seem to eat them, and that they contain substances and compounds known to be beneficial from a "generic" nutritional standpoint- you know, like in humans.

All well-meaning, not intended to do harm to consumers. I'm sure...but perhaps occasionally, just a bit of a stretch, IMHO.

I just wonder if we stretch and assert too much sometimes?

I'm not saying that it's "bad" to make inferences (we do it all the time with various topics- but we qualify them with stuff like,  "it could be possible that.." or "I wonder if..."), but I can't stand when absolute assertions are made without any qualification that, just because this leaf has some compound which is part of a family of compounds that are thought to be useful to shrimp, or that shrimp devour them...that it's a "perfect" food for them. 

It's just a food- one of many possibilities out there.

Of course, I hope I'm not out there adding to the confusion! We try to hold ourselves to higher standards on this topic; yet, like so many things we talk about in the world of botanicals, there are no absolutes here.

What is fact is that some botanical/plant-derived materials, such as various seeds, root vegetables, etc., do have different levels of elements such as calcium and phosphorous, and widely varying crude protein. Stuff that's known to be beneficial to shrimp, of course. These things are known by science. Yet, I have no idea what some of the seed pods we offer as botanicals contain in terms of proteins or amino acids, and make no assertions about this aspect of them, above and beyond what I can find in scientific literature.

However, I suppose that one can make some huge over-generalizations that one seedpod/fruit capsule is somewhat similar to others, in terms of their "profile" of basic amino acids, vitamins, trace elements, etc. (gulp). We can certainly assume that some of this stuff, known to have nutritional value, can possibly make these materials potentially useful as a supplemental food source for fishes and shrimps.

Yet, IMHO that's really the best that we can do until more specific, scientifically rigid studies are conducted.

Now, we may not know which seed pods and such in and of themselves are more nutritious to fishes and shrimp than others, but we DO know from simple observation that some are better at "recruiting" materials on their surfaces which serve as food sources for aquatic organisms!

There is little disagreement on this topic.

Yeah, I'm talking about the biofilms and fungal growth, which make their appearance on our botanicals, leaves, and wood after a few weeks of submersion...

As we've talked about ad nauseam here, biofilms are not only typically harmless in aquariums, they are utilized as a supplemental food source by a huge variety of fishes and shrimps in both Nature and the aquarium. They are a rich source of sugars and other nutrients, and could prove to be an interesting addition to a "nursery tank" for raising fry if kept in control. Like, add a bunch of leaves and botanicals, let them do their thing, and allow your fry to graze on them!

Don't believe me?

Ask almost any shrimp keeper-they'll "sing the praises" of biofilm for the "grazing" aspect!

And of course, it's long been known from field studies that as leaves and other plant materials break down, they serve as "fuel" for the growth of biofilm, fungi and microorganisms...which, in turn, provide supplemental food for our fishes. I've seen a bunch of videos of shrimps and fishes in the wild "grazing" over fields of decomposing leaves and the biofilms they foster.

And we know from years of personal experience and observation in the aquarium that fishes and shrimp will consume them directly, removing them from virtually any surface they form on.

And some materials are likely better than others at recruiting and accumulating biofilm growth. The "biofilm-friendly" botanical items seem to fall into several distinct categories: Botanicals with hard, relatively impermeable surfaces,  softer, more ephemeral botanical materials which break down easily, and hard-skinned botanicals with soft interiors, and...

Okay, wait- that kind of covers like, everything, lol.


What that tells ME, the over-caffeinated, perhaps somewhat under-educated armchair "aquatic ecologist-wannabe", is that most of the botanicals we play with- in addition to being potentially consumed directly by aquatic organisms- likely also have some capability of recruiting biofilms.

And the idea of biofilms and such being an excellent supplemental food source for shrimp-and fishes- is not's just something that we're finally getting around to agreeing about with our little friends! (And with the shrimp people, too)

And don't get me started about fungal growths...

Fungal growth in aquatic environments is absolutely essential for the function of the ecosystem. Scientists have determined that as much as 15% of the decomposing leaf biomass in many aquatic habitats is "processed" by fungi, according to one study I found.

Yes, fungi. Again.

Fungi tend to colonize wood and botanical materials, because they offer them a lot of surface area to thrive and live out their life cycle. And cellulose, hemicellulose, and lignin- the major components of wood and botanical materials- are degraded by fungi which posses enzymes that can digest these materials! Fungi are regarded by biologists to be the dominant organisms associated with decaying leaves in streams, so this gives you some idea as to why we see them in our aquariums, right?

In aquairum work, we see fungal colonization on wood and leaves all the time. Most hobbyists will look on in sheer horror if they saw the extensive amount of fungal growth which occurs in the wild on their carefully selected, artistically arranged wood pieces! Yet, it's one of the most common, elegant, and beneficial processes that occurs in Nature!

And fungi are absolutely food for a huge variety of aquatic organisms- including fishes and shrimp.

 Like, everyone. 

Biofilms and fungi just don't appear out of thin air, though.

Most of these life forms enter into aquatic "food webs" in the form of...wait for it...detritus! Yup, both fine and course particular organic matter are a main source of these materials. I suppose this explains why heavy accumulations of detritus and algal growth in aquaria go hand in hand, right? Detritus is "fuel" for life forms of many kinds.

Think about this when you set up your next botanical-style aquairum:

Incorporating botanical materials in our aquariums for the purpose of creating the foundation for biological activity is the starting point. Leaves, seed pods, twigs and the like are not only "attachment points" for bacterial biofilms and fungal growths to colonize, they are physical location for the sequestration of the resulting detritus, which serves as a food source for many organisms, including our fishes.

Consider: Every botanical, every leaf, every piece of wood, every substrate material that we utilize in our aquariums is a potential component of... food production!

The initial setup of your botanical-style aquarium will rather easily accomplish the task of facilitating the colonization of said biofilms and fungal growths. There isn't all that much we have to do as aquarists to facilitate this but to simply add these materials to our tanks, and allow the appearance of these organisms to happen. 


And we shouldn't obsess over removing every single bit of detritus, fungi, uneaten food etc. Yeah, to facilitate these aquarium "food webs", we need to avoid going crazy with the siphon hose! Simple as that, really! When you remove some of this stuff, you're literally stealing food from someone's "mouth" (or hyphae, if your a fungi!)

Yeah, the idea of embracing the production of natural food sources in our aquariums is elegant, remarkable, and really not all that surprising. They will virtually spontaneously arise in botanical-style aquariums almost as a matter of course, with us not having to do too much to facilitate it.

What about fry?

Can't the botanical-style aquarium, replete with its compliment of leaves, botanicals, and their resulting biofilms and fugal growths feed batches of fish fry easily?I think so. Our tanks seem like they could be the ultimate "nursery" for fry!

Everyone who breeds fishes has their own style of fry rearing.

Some hobbyists like bare bottom tanks, some prefer densely planted tanks, etc. I'm proposing the idea of rearing young fishes in a botanical-style aquarium filled with leaves, some seed pods, and maybe some plants as well. They physically and "functionally" mimics, at least to some extent, the habitats in which many young fishes grow up in.

My thinking is that decomposing leaves will not only provide material for the fishes to feed on and among, they will  foster the aforementioned biofilms and fungal growths, and provide a natural "shelter" for them as well, potentially eliminating or reducing stresses. In Nature, many fry which do not receive parental care tend to hide in the leaves or other "biocover" in their environment, and providing such natural conditions will certainly accommodate this behavior.

Decomposing leaves can stimulate a certain amount of microbial growth, with "infusoria" and even forms of bacteria becoming potential food sources for fry. I've read a few studies where phototrophic bacteria were added to the diet of larval fishes, producing measurably higher growth rates. Now, I'm not suggesting that your fry will gorge on beneficial bacteria "cultured" in situ in your blackwater nursery and grow exponentially faster.

However, I am suggesting that it might provide some beneficial supplemental nutrition at no cost to you!

I've experimented with the idea of "onboard food culturing" in several aquariums systems over the past few years, which were stocked heavily with leaves, twigs, and other botanical materials for the sole purpose of "culturing" (maybe a better term is "recruiting) biofilms, small crustaceans, etc. via decomposition. I have kept a few species of small characins in these systems with no supplemental feeding whatsoever and have seen these guys as fat and happy as any I have kept.

And it's the same with that beloved aquarium "catch all" of "infusoria" we just talked about...These organisms are likely to arise whenever plant matter decomposes in water, and in an aquarium with significant leaves and such, there is likely a higher population density  of these ubiquitous organisms available to the young fishes, right?

Now, I'm not fooling myself into believing that a large bed of decomposing leaves and botanicals in your aquarium will satisfy the total nutritional needs of a batch of characins, but it might provide the support for some supplemental feeding! On the other hand, I've been playing with this recently in my "varzea" setup, stocked with a rich "compost" of soil and decomposing leaves, rearing the annual killifish Notholebias minimus with great success.

It's essentially an "evolved" version of the "jungle tanks" I reared killies in when I was a teen. A different sort of look- and function! The so-called "permanent setup"- in which the adults and fry typically co-exist, with the fry finding food amongst the natural substrate and other materials present in the tank. Or, of course, you could remove the parents after breeding- the choice is yours. I admit that it's not the most "efficient" way to rear frying large numbers, but it's a cool experiment!

I'd take the concept even a bit further by "seeding" the tank with some Daphnia, Cyclops and perhaps some of the other commonly available live freshwater crustaceans and copepods, and letting them "do their thing" before the fry arrive. This way, you've got sort of the makings a little bit of a "food web" going on- the small crustaceans helping to feed off of some of the available nutrients and lower life forms, and the fish at the top of it all. 

Now, granted, I'm totally romancing this and perhaps even over-simplifying it a bit. However, I think that there is a compelling case to be made for creating a rearing tank that supports a biologically diverse set of inhabitants for food sources.

The basis of it all would be leaves and some of the botanicals which seem to do a better job at recruiting biofilms- the "harder shelled/surfaced" stuff, like  Jackfruit leaves, Yellow Mangrove leaves, Guava Leaves, Carinaina Pods, Dysoxylum pods, etc...I think these would be interesting items to include in a "nursery tank." And of course, they provide shelter and foraging areas and impart some tannins into the water...the "usual stuff."

It's fun to play with new ideas- or evolve old ones such as this. Obviously, this isn't be the "ultimate" fry-rearing technique; however, it's just another one of those ideas to have in our "arsenal" of skills that would be fun for serious-or casual- fish breeder to experiment more with.

I think it's one we have seriously legit basis for playing with more and more!

Nothing is wasted in Nature, right?

In the wild aquatic habitats we love so much, food webs are vital to the organisms which live in them. They are an absolute model for ecological interdependencies and processes which encompass the relationship between the terrestrial and aquatic environments.

We should embrace this in our aquarium work, and do our best to facilitate the processes which can lead to the development of "food webs" in our tanks, for fishes at all stages of life. The botanical style aquarium is literally "optimized" to provide benefits such as food production, by the very existence of its "operating system"- decomposing botanical materials!

Let's take advantage of this!

Let's try not to make too many assumptions and assertions- at least, not without doing some of our own research and "field work."

As hobbyists, let's continue to experiment, observe, learn from, and share our experiences and observations with others. 

We all win from that.

In fact, that's likely the one absolute assertion I will make!

Stay curious. Stay disciplined. Stay objective. Stay experimental. Stay creative...

And Stay Wet.


Scott Fellman

Tannin Aquatics 





Evolving techniques

It's kind of fun to make little "tweaks" or adjustments to our aquarium methodology or approaches to how we do certain things. This is what pushes the state of the art in aquaristics further down the road. Now, not every one of these adjustments is a quantum leap forward, at least, not initially. Many are simply subtle iterations of things we've played with before.

An example?

One of our fave approaches, sort of derived out of our "Urban Igapo" work, has been to "dry set" the aquarium.  A sort of technique I call the "transitional approach." 

Basically, all you're doing is adding the prepared botanicals and leaves to your aquarium before it's filled, and spraying them down with water and our sprayable Purple Non-Sulphur bacterial inoculant, "Nurture" to kick-start the biological processes. Let it sit. Spray it down daily.

Then fill it.

Unlike in our "Urban Igapo" approach, you're not trying to grow terrestrial grasses or plants during the "dry phase." You're simply creating and managing  what will ultimately be the submerged habitat in your aquarium for a while before filling it.

I've done this a number of times and had great results.

Stupidly simple. Yet, profoundly different.


Because, rather than our "traditional" approach of adding the botanicals and leaves to the aquarium after it's already filled, you're sort of replicating what happens in Nature in the wild when forest floors and other terrestrial environments are inundated by overflowing streams and rivers.

The thing I like about this approach (besides how it replicates what happens in the wild) is that it gives you the ability to really saturate and soften  the botanicals and leaves, and to begin the process of decomposition and bacterial colonization before you add the water. 

When do you fill the aquarium?

You can wait a few days, a week or two, or as long s you'd like, really. The idea is to get the materials physically placed, and to begin the process of colonization and "softening" by fungi and bacterial biofilms- known as "conditioning" by ecologists who study these habitats. 

And of course, fishes and invertebrates which live amongst and feed directly upon the fungi and decomposing leaves and botanicals will contribute to the breakdown of these materials as well! Aquatic fungi can break down the leaf matrix and make the energy available to feeding animals in these habitats. And look at this little gem I found in my research:

"There is evidence that detritivores selectively feed on conditioned leaves, i.e. those previously colonized by fungi (Suberkropp, 1992; Graca, 1993). Fungi can alter the food quality and palatability of leaf detritus, aecting shredder growth rates. Animals that feed on a diet rich in fungi have higher growth rates and fecundity than those fed on poorly colonized leaves. Some shredders prefer to feed on leaves that are colonized by fungi, whereas others consume fungal mycelium selectively..."

"Conditioned" leaves, in this context, are those which have been previously colonized by fungi! They make the energy within the leaves and botanicals more available to higher organisms like fishes and invertebrates! 

We've long maintained that the appearance of biofilms and fungi on your botanicals and wood are to be celebrated- not feared. They represent a burgeoning emergence of life -albeit in one of its lowest and most unpleasant-looking forms- and that's a really big deal. 

"Oh shit, he's going to talk about biofilms AGAIN!"

Well, just for a second.

Biofilms, as we probably all know by now, form when bacteria adhere to surfaces in some form of watery environment and begin to excrete a slimy, gluelike substance, consisting of sugars and other substances, that can stick to all kinds of materials, such as- well- in our case, botanicals. It starts with a few bacteria, taking advantage of the abundant and comfy surface area that leaves, seed pods, and even driftwood offer.

The "early adapters" put out the "welcome mat" for other bacteria by providing more diverse adhesion sites, such as a matrix of sugars that holds the biofilm together. Since some bacteria species are incapable of attaching to a surface on their own, they often anchor themselves to the matrix or directly to their friends who arrived at the party first.

It's a literal explosion of life. It's a gift from Nature. And we can all receive it and benefit from it! 

Another advantage of this approach? The traditional "cycling" time of a new tank seems to go much faster. Almost undetectable, in many of my experiments. I can only hypothesize and assume that it's likely a result of all of the bacterial growth in the "terrestrial" phase, and the concurrent  "conditioning" of the botanical materials.  

Tannin's creative Director, Johnny Ciotti, calls this period of time when the biofilms emerge, and your tank starts coming alive "The Bloom"- a most appropriate term, and one that conjures up a beautiful image of Nature unfolding in our aquariums- your miniature aquatic ecosystem blossoming before your very eyes!

The real positive takeaway here: Biofilms are really a sign that things are working right in your aquarium! A visual indicator that natural processes are at work, helping forge your tank's ecosystem.

So, what about the botanicals?

The idea of utilizing botanicals in the aquarium can be whatever you want, sure. However, if you ask me (and you likely didn't)- the idea of utilizing these materials in our tanks has always been to create unique environmental conditions and foster a biome of organisms which work together to form a closed microcosm. That is incredible to me.

And the idea of "dry setting" your botanical materials and sort of "conditioning" them before adding the water, this "transitional approach", while not exactly some "revolutionary" thing, IS an evolutionary step in the development of botanical-style aquarium keeping.

The "transitional approach" is definitely a bit different than what we've done in the past, and may create a more stable, more biologically diverse aquarium, because you're already fostering a biome of organisms which will make the transition to the  aquatic habitat and "do their thing" that much more quickly.

This IS unique.

We're talking about actually allowing some of the decomposition to start before water is ever added to our tanks. It's a functional approach, requiring understanding, research, and patience to execute. There's really nothing difficult about it.

And the aesthetics? They're going to be different than what you're used to, no doubt. They will follow as a result of the process, and will resemble, on a surprisingly realistic level, what you see in Nature.

But the primary reason is NOT for aesthetics... 


The interactions and interdependencies between terrestrial and aquatic habitats are manifold, beneficial, and quite compelling to us as hobbyists. To be able to study this dynamic first hand, and to approach it somewhat methodically, is a significant change in our technique.

And yeah, it's almost absurdly easy to do.

The hard part is that it requires a bit more patience; not everyone will see the advantages, or value, and the trade-off between waiting to fill your tank and filling it immediately. It may not be one that some are willing to make.

If you do, however, you will get to see, firsthand, the fascinating dynamic between the aquatic and the terrestrial environment in a most intimate way.

It could change your thinking about how we set up aquariums. 

It could.

At the most superficial level, it's an acknowledgement that, after many decades, we as hobbyists are acknowledging and embracing this terrestrial-aquatic dynamic. It's a really unique approach, because it definitely goes against the typical "aquatic only" approach that we are used to.



When you consider that many aquatic habitats start out as terrestrial ones, and accumulate botanical materials and provide colonization points for various life forms, and facilitate biological processes like nutrient export and production of natural food resources, the benefits are pretty obvious. Again, the "different aesthetics" simply come along as "part of the package"- both in Nature and in the aquarium.

Replicating this process and managing it in the aquarium also provides us as hobbyists highly unique insights into the function of these habitats. 

From a hobby perspective, evolving and managing a closed ecosystem is really something that we should take to easily.

Setting up an aquarium in this fashion also provides us with the opportunity to literally "operate" our botanical-style aquariums; that is, to manage their evolution over time through deliberate steps and practices is not entirely unknown to us as aquarium hobbyists.

It's not at all unlike what we do with planted aquarium or reef aquarium. In fact, the closest analog to this approach is the so-called "dry start" approach to planted aquariums, except we're trying to grow bacteria and other organisms instead of plants.

Yes, it's an evolution.

Simply, a step forward out of the artificially-induced restraints of "this is how it's always been done"- even in our own "methodology"- yet another exploration into what the natural environment is REALLY like, how it evolves, and how it works- and understanding, embracing and appreciating its aesthetics, functionality, and richness.  

Earth-shattering? Not likely.

Educational? For sure.

Thought provoking and fun? Absolutely.

A simple, yet I think profound "tweak" to our approach.

Stay curious. Stay open-minded. Stay thoughtful. Stay observant. Stay creative.

And Stay Wet.


Scott Fellman

Tannin Aquatics 


May 18, 2021



There are as many approaches to setting up aquarium as there are aquarists. Sure, there are a few "best practices" and such which you could pretty much count on, and then there are some new approaches and steps you can take, based upon our collective newer experience, which is changing daily.

We talk quite a bit about the process of setting up a botanical-style, blackwater aquarium from scratch, and the mindset, research, concepts, and execution involved. However, we have a large number of customers and community members who have an existing aquarium and want to switch it over to a blackwater aquarium. We receive a fair number of questions about the process, so I figured that now is as good a time as any to touch on it!

Now, I've always had this "thing" about most aquarium-related "how-to" type articles, because I think they tend to offer up information as if everything were simply a "recipe", and that if you "do this" or add "a bit of that"- you're certain to achieve "such-and-such" a result...And you know as well as I do that, with hundreds of possible variables in the equation, an aquarium is no "picnic."

Nothing is a "given", even when you're considering trying to hit a narrow range of conditions with seemingly "the right" combination of actions.

So, with that "disclaimer" in mind (LOL), we're going to at least look at the overall "how to", and we can all fill in the blank spaces in our specific situations with more customized approaches as needed.

First off, the obvious questions we need to ask ourselves when commencing such a change are, "Do the fishes which I keep come from this type of environment in nature?" and "Am I willing to take the time to do it slowly?" The answer to the first question is pretty obvious- and it's almost sort of insulting that I'd even mention it...but due diligence, ya' know...

The second question is to me- more fact, it's, as we say here in America- "The whole ball game.." (they probably say that in every country, too, but hey...).

You must employ patience. You have to take the time. There is simply nothing to be gained by rushing this process.

It goes without saying that, if you've been keeping your fishes- even ones which come from blackwater conditions in Nature- in harder, more alkaline water, there will need to be a gradual transition to this type of environment. Although fishes are quite adaptable, significant environmental changes are tough on fishes, and they need to be made slowly.

We've talked about it before, but I am also of the opinion that even, for example, Tetras or other fishes that may have been bred commercially in "tap water" conditions (not necessarily soft and acidic) for the past few decades still could benefit from being "repatriated" into more natural conditions. I don't believe that a few dozen generations of captive breeding could erase the genetic adaptations that these fishes have made through evolution over eons.

That being said, and the lofty goal of replicating "natural conditions" aside, however, you're still putting your fishes from a stable situation through an environmental change, and this requires time. It's something that needs to be done carefully and thoughtfully, over several weeks, IMHO.

I suppose the most fundamental, absurdly obvious question is, do you want to lower the pH of the water, and if so, why?And, is this a good idea? Is it something that you feel will benefit your fishes?

Yes, seemingly dumb questions, but when you're embarking on a paradigm-shifting environmental change to an existing tank, and all of its inhabitants, it's important to give this a lot of thought. If you're just doing it to be part of the (fictitious) "Sub 6.5pH Club", or to humble brag on Instagram, or do a video on Tik Tok about your "cool soft, acidic water "or whatever- you need to reassess things.

Once you've been able to address that fundamental issue, the next steps are perhaps the most important ones.

I'd start the conversion process by doing a sort of "baseline assessment" of the pH and alkalinity of my water. I'd make sure that I have sufficient filtration in place to accommodate some additional bioload (you know, decomposing leaves and such). You should also give some thought about what your target pH/alkalnity are. If you're using tap water with a pH of 8.2 and considerable carbonate hardness, for example, you need to consider how you might bring these measurements down.

If you're using a substrate which is known to buffer the water, it's going to make the process of lowering the pH significantly an extremely challenging, if not nearly impossible, process. You may consider a total substrate switch- another process which can add extreme stress and biological challenges to your system. It's literally a "go/no go" item, IMHO. It may simply necessitate breaking down the tank completely and starting over...


And you should, in my opinion, be willing to make the "infrastructure investment" (pricy though it may be) in a reverse osmosis/dioinization unit...or at least, finding a source of good, consistent RO/DI water (many fish stores will sell you RO/DI by the gallon/litre!). The rationale here is that it's far, far easier to reduce the pH in water with little or no carbonate hardness...a better "canvas" upon which to work.

If you aren't using RO/DI water in your current setup, you can even start gradually mixing some in (without adjusting it or adding anything) with your regular water exchanges. This will help to gradually lower the carbonate hardness and pH. Slow steps. If you can get your water to around neutral (7.0), that's a great "stepping off point" for modifications to lower pH levels.

Now, speaking of pH- I know it's an obsession of lots of hobbyists... SO, here's the deal: I wouldn't "shoot for the stars" and try to get to 5.5 or something really low right out of the blocks. For that matter, I wouldn't obsess over ANY specific "target number", really...Rather, I'd try to find a tight range that you could easily maintain. With the understanding that you need to do this over a period of weeks-months, even...I'd shoot for a modest pH level of like 6.7-6.5 as your target range...Get a feel or operating a tank under these conditions and maintaining them consistently. 

Once you've got a sort of handle on the pH and alkalinity, and have gotten them "in range", you can begin the (slow) process of "fine tuning" your habitat. Now, you might be (as I often am) surprised to find that botanicals and leaves, while impactful somewhat on pH, will drop levels much more slowly, and to a lesser extent than you might think.

And as I've mentioned many times over the years, if you have harder, alkaline water, the impact will be even more minimal. And the impact on carbonate hardness from botanicals is essentially nothing, in my experience. You simply need to utilize other methods to reduce KH (like the aforementioned use of RO/DI water).

The other, probably insultingly obvious thing to be aware of is that, even if the water looks dark brown, it's not necessarily 6.3 and zero KH. I mean, tannins will stain water in the absence of chemical filtration media to remove them. They may not significantly impact the pH, as mentioned above, but you'll get that "visual" tint. And I know many hobbyists who are perfectly happy with that. Hard, alkaline tinted water is aesthetically beautiful, and the benefits of humic substances imparted by botanical materials may still be realized.

I am not aware of any studies done on the health impact to tropical fishes of tannins and humic substances in harder, alkaline environments versus soft, acidic ones, so it's sort of an open topic, really. Perhaps one that you could make meaningful observations about!

When "transitioning" an existing aquarium, my tendency is to initially start with relatively small quantities of materials, usually leaves, and then work in the more durable botanicals like seed pods and such. I guess my thought process is that materials such as leaves tend to break down more quickly, imparting their humic acids and tannins into the water at a corresponding pace.

And of course, after your initial additions, you should measure pH and carbonate hardness again, to see if there has been any impact. A lot of hobbyists are into checking TDS as well...we've beaten up that subject quite a bit in past blogs here, so it's something you might want to research.

In addition, the more rapid decomposition of the leaves fosters more biological activity (ie; beneficial bacteria, fungal growths, etc.)

The botanical-style aquarium is a microcosm which depends upon botanical materials to impact the environment.

This microcosm consists of a myriad of life format all levels and all sizes, ranging from our fishes, to small crustaceans, worms, and countless microorganisms. These little guys, the bacteria and Paramecium and the like, comprise what is known as the "microbiome" of our aquariums.

A "microbiome", by definition, is defined as "...a community of microorganisms (such as bacteria, fungi, and viruses) that inhabit a particular environment." (according to Merriam-Webster)

Now, sure, every aquarium has a microbiome to a certain extent. The long-term successful botanical-style aquarium is 100% dependent upon the formation and growth of a healthy microbiome.

We have the beneficial bacteria which facilitate the nitrogen cycle, and play an indespensible role in the function of our little worlds. The botanical-style aquarium is no different; in fact, this is where I start wondering...It's the place where my basic high school and college elective-course biology falls away, and you get into more complex aspects of aquatic ecology in aquariums.

Yet, it's important to at least understand this concept as it can relate to aquariums. It's worth doing a bit of research and pondering. It'll educate you, challenge you, and make you a better overall aquarist. In this little blog, we can't possibly cover every aspect of this- but we can touch on a few broad points that are really fascinating and impactful.

So much of this process-and our understanding starts with...botanicals. 

Obviously, the question here is, "How much stuff do I start with?" And of course, my answer is...I have no idea. Yeah, what a shocker, right? I realize that's the least satisfying, possibly least helpful answer I could give to this question. Or is it? I mean, taking into account all of the possible variables, ranging from the type of water your starting with, to what kind of substrate material you're using, it would be a shot in the dark, at best.

My advice is to start with conservatively small quantities of, maybe a half a dozen leaves for every 15 US gallons (56.78L) of water. Maybe a similar amount of seed pods. You might not even notice any difference..or you might see a .2 reduction in have to test. I recommend a digital pH meter for best accuracy. In fact, I recommend digital meters for almost everything, especially considering the tinted water which our aquariums feature, rendering the results of liquid test kits challenging to interpret.

I would make it a habit to add the same amount of materials (leaves initially, and pods if you want to mix 'em in on subsequent additions) at a regular interval. Say, every 4 or 5 days. Test again. See where you're at. I would tend to shoot for not reducing your pH by more than .5 per week. That's me of course...your fishes' tolerance and your personal comfort level with doing so is your call. And it's really a matter of repeating this process until you hit your desired range. Notice I said "range" and not "target pH" or whatever?

Personally, I've experienced far better results at manipulating pH in my water holding containers than I have in the aquarium. Of course, the dynamic of "transitioning" an aquarium from hard and alkaline to soft and acidic is a process which occurs in both the tank and the source water containers...

We receive a lot of questions about utilizing chemical filtration media while using botanicals, and again, there is no "right or wrong" here. I will tell you from my personal experience that I like to use filtration materials like Seachem "Renew", small amounts of activated carbon ("Seriously, Fellman? Activated carbon" Yes, really.), and Poly Filter on a full-item basis in my systems.


The reality is that organic scavenger resins, carbons, and materials like "Renew" might be indiscriminate in their removal of stuff like humic substances, tannins, and other organic compounds released by the botanicals, but they also tend to moderate things you don't want, like ammonia and "miscellaneous" organics (how's that for a "cop out" on my part...falling back on "generics!").

Yeah, they might remove some of the visual tint, but they will remove a lot less of it if you don't use the recommended "dose" per gallon. And frankly, I've never done a serious test to see exactly how much of whatvarious chemical filtration media actually remove from the water. Being honest here...I"ll bet not too many of you have, either, right? So, we're kind of relying on the manufacturer's instructions and good old observation!


If you're getting a sort of feeling that this is hardly a scientific, highly-choreographed, one-size-fits-all're totally right. It's really a matter of (as the great hobbyist/author John Tullock once wrote) "test and tweak." In other words, see what the hell is going on before making adjustments. Logical and time-testing aquarium procedure for ANY type of tank! 

Now, the interesting thing that I've always found with my botanical-style, blackwater aquariums is that they tend to find their own "equilibrium" of sorts- a stable "operating range" that, once you find yourself doing the same procedures (i.e.; regular, consistent water exchanges, additions of botanicals, and media replacement, etc.) at regular intervals, tends to remain highly consistent as long as you keep them up.

I've talked repeatedly about the (IMHO mostly unwarranted) fears people have about precipitous pH "drops" and "crashes" and such, and I believe that most all of these things are mitigated by consistency, patience, taking small steps, testing regularly, documenting and repeating them.

I've said it before an I will repeat it once again: I believe that pretty much every one of the "anomalous" pH "crashes"/disasters I've heard of in regards to blackwater, botanical-style tanks has been directly attributable to "operator error"- i.e.; failing to be consistent, diligent, and conservative. Tanks simply don't "crash" by themselves, in my experience.

They fail as a result of something that we did or did not do: Failure to slow down. Failure to measure. Failure to observe or continue to follow procedures that have been giving us consistently good results. In my experience, tanks will typically show "signs", develop trends, and demonstrate the manifestations of "issues" gradually...if you're attuned to them.

Botanical-style blackwater aquariums are not "set and forget" systems, exactly like reef aquariums, planted "high tech" tanks, Mbuna systems, Discus tanks, etc. You need to observe and "pivot" as situations dictate. A sort of "yin and yang", if you will, between pushing the limits and playing it safe... And you have to ask yourself if this type of "active tank management" lifestyle is for you! 

Now, within the "Things are awesome!" range and "Oh shit!" range, there is a ton of room for experimentation and research. "Best practices" in terms of how much stuff to add, when to add it- when (or if) to remove it, etc. are still the subject of much discussion among members of our community, and are evolving daily.

There are, as we mentioned before- no specific "recipes" to follow...only those emerging "best practices" developed by those of us who have ventured along this path. We can tell you about the benefits, show you how to prepare botanicals, advise you about husbandry, and warn you of the things that can go wrong. The rest is up to us as individual hobbyists.

And that's not only the challenge- but (in my opinion) the appeal- of this aquarium specialty. We all have an opportunity to contribute to the state of the art. To increase our body of knowledge of how these systems operate. To unlock the manifold benefits- and potential pitfalls- of botanical-style aquarium "practice."

It's not for everyone. Not everyone likes the look. Not everyone likes the work and effort required. There are still many "unknowns" and no one way to achieve "success." However, for those who choose to walk on this most interesting path- the potential rewards for us- and most important- for our fishes- are huge.

This piece was, out of necessity, the most cursory look at this topic of "transitioning", but I hope it opens up more discussion on this seemingly popular topic within the aquarium community.

Stay excited. Stay conservative. Stay experimental. Stay diligent. Stay skeptical. Stay hopeful. Stay thoughtful...

And Stay Wet.

Scott Fellman

Tannin Aquatics 





May 17, 2021


When dreams come alive...

One of the interesting things about being a fish geek is that we have lots of amazing ideas and dreams, and it's possible to act on so many of them!

Do you have one of those "perfect ideas" for a tank floating around in your head? The kind which, although not necessarily crazy difficult/expensive to do- just something that you've been itching to try. Something aspirational, or otherwise goal-worthy.

My aquarium journey has been as much about dreaming as it has been about executing.

Seems like I'm always coming up with "perfect ideas" for crazy displays- you know, like biotope-inspired themes, specialized systems for particular fishes, etc....but I never seem to get to all of them. I don't think I'm at all unique in that regard. I think a lot of us have that "perfect tank" in our heads, and we're waiting for factors like time, money, or the right livestock to come our way in order to execute them.

As a young hobbyist, I never could afford anything, so I would fall asleep scheming up these dream tanks in my head...Some of these ideas were insane. Just impossible to execute at the time. Others were very realistic, entirely achievable, and as I grew older and had the capability, I was able to build them them.

And often, when I was finally able to build some ofhtese "dream tanks", it would come to pass that I didn't enjoy having the tank as much as I enjoyed scheming it!

Why is that?

Some dreams are just meant to be...dreamed, I suppose. Right?

And then there was blackwater.

For some reason, this type of tank really resonated in me. Since I was a kid. It was so...weird- I mean, a tank with water so dark that you couldn't always see the fishes clearly. It seemed so "anti-establishment" for this teenage fish geek...Maybe that was the start of my experimentation with these kinds of tanks. I began with peat moss in my killie tanks, then played around with sticks and leaves and before you know it, I had Neon Tetras spawning- stuff like that!

My dreams took me in a new direction.

The reef keeping bug hit in the mid eighties, and I was enamored. I mean, keeping LIVE CORALS! Whoa! Yeah, my first "minireef" was a hastily planned affair, based on George Schmitt's groundbreaking 1986 series in Freshwater and Marine Aquarium magazine, with tons of the macro algae Caulerpa, some mushroom anemones, and I think a Sinularia soft coral, with Pulsing Xenia.

For a 30-gallon tank for a teenager, it was surprisingly badass!

And that started a decades-long affair with reefs, which eventually led me to a writing/speaking career, hobby "fame", aquarium design gigs, and the opportunity to become a partner in the launch of a coral propagation/importation business, Unique Corals.

Unique was an astonishing success in our industry, and I was quite proud to be associated with it. We set a high standard, created a terse manifesto for sustainability- and walked the walk.

Yet, I always stayed in touch with the FW world, although my time and focus were on reefs and corals..Yet, in the back of my mind...I kept thinking of those cool tanks I would scheme about as a teenager.

Those crazy freshwater concept ideas that I loved so much. The freshwater world, as seen from the "salty side"of the fence, although evolved highly since I played in it actively, still needed some new ideas, in my opinion.

Different stuff.

Those dreams again.

It was also the point where I realized that reef aquariums and the reef hobby, although amazing and fascinating, were somehow getting a bit-well-monotonous for me.

I mean, they're awesome, but dealing with corals every day, and some of the disturbing (to me) "cultural shifts" in coral side of the reef-keeping community, such as a sort of "commoditization" and "branding" of corals, and a seemingly anemic interest in recreating the habitat aspects of reefs in our homes (short of just buying a lot of gadgetry) really turned me off.

It brought me back to the realization that freshwater had so many more possibilities for me- many which I had never even considered before.

Yeah, the dreams were calling.

So I made the decision to act on those dreams.

In a move that shocked a lot of people in the reef keeping world, I sold my interest in the thriving UC (which is still at the top of its game, btw) to "come home" to the beckoning freshwater world, filed with ideas and enthusiasm once again...And Tannin Aquatics was born.

And you know, those dreams were happening again...I was scheming new aquariums and concepts all the time. It felt pretty cool.

One of my favorite things about the hobby is that we can dream up/scheme up all sorts of wacky ideas, think through them...and maybe, just maybe, build them. Some are totally outlandish and push the envelope of what is even technically possible...

And I think that's important. Trying to figure out how to replicate the function of wild habitats- not just the look- is a huge step forward. It requires a lot of thinking, research, and mental shifts to accept things- which previously might have scared us- as "okay."

Looking at Nature as a guide for how to model its function, not just as an aesthetic inspiration. Especially when the "aesthetics" of a natural habitat are far, far different from the "conventional" hobby interpretation of what we think Nature looks like.

Lately, I've been sharing a lot of pics of some of our more esoteric, unconventional aquariums on our social media feeds. Interestingly, the response from the community has been overwhelmingly positive; like, almost every response is kind of "Cool, I love that!" or, "I really want to do a tank like that!" 


These responses are so different from what we would see a few years back, when the typical response to a pic like that was literally, "That tank looks dirty." or (my fave) "Is that the before shot of a re-scape?"

Yeah, we've come a long way.

Dreams, mental shifts, and accepting new ideas go hand in hand.

Yet, even after all of the exposure botanical-style aquariums have received, there is still some concern, hesitation- or whatever you want to call it, about setting up an aquarium with a huge amount of leaves and seed pods and stuff. I totally understand why; Adding all sorts of biological material to an aquarium requires a population of organisms in place to process it.

We've talked extensively about what happens in Nature (and in our tanks, really) when leaves and botanicals are added to water. However, no amount of me explaining that a community of life forms will process them (if you let them) will make some people feel comfortable about the idea.

The biggest mental shift that we have to make in this hobby specialty is to understand that the leaves, seed pods, etc. are not just aquascaping "set pieces", put in play to achieve a "look." Rather, that they are a functional part of the aquarium's environment, hosting a myriad of life forms which drive the ecology of the tank. In essence, they're part of the "operating system" that is essential for successful long-term function of the botanical-style aquarium.

It's tough to get this point across sometimes.

We're so immediately attracted to the look of these aquariums that we can easily lose sight of the fact that the look is the by-product of the function. I receive so many emails and DM's from hobbyists new to the botanical "game", asking if they should "scrape off" the "gunk" that is showing up on their leaves and seed pods that I think this is a real "thing" that we as a community need to discuss again and again and again.

The idea is NOT to remove this stuff. It's NOT to siphon out the decomposing materials. It's about letting Nature take some of the control.


It's perhaps the most challenging aspect of the botanical-style aquairum movement.

It's about linking the aspirational nature of dreams with the necessities of reality.  

And trust me, practicality and dreams go surprisingly well together!

With so many cool hobbyists doing so many cool things, it's amazing to see all of the action happening around me. I'm very privileged to hear about your dreams...Some of the types of tanks and ideas you're coming up with are nothing short of amazing. I've gotten to supply botanicals for everything from Geophagus biotope aquariums, to permanent killifish displays, public aquairums, universities doing research, to Axolotls, fish breeding systems, and vivarium displayss!

Super crazy cool projects across the full spectrum of the freshwater aquarium hobby world. And it's just beginning. 

That's where following my aquarium dreams, and making them come alive, has taken me.

So when those dreams advice, cliche'd though it may to listen to them; act on them. You never know where they might take you.

Today's very simple thought.

Keep dreaming. Make those mental shifts. And dream some more.

Stay imaginative. Stay engaged. Stay creative. Stay thoughtful...

And Stay Wet.


Scott Fellman

Tannin Aquatics.





May 14, 2021


Born and Bred

The other day I was admiring some of my Epiplatys dageti Monroviae (a top-spawning African killifish) spawning in one of my tanks. It's always cool to see your fishes spawn, and it's even more cool when they are fish that you've raised from fry themselves- I guess it's something about "closing a circle", or whatever. 

Regardless, the satisfaction of seeing our fishes- any of our fishes- engage in reproductive behavior in our aquariums is not only one of Nature's wonders- it's kind of a testimony to our work!

When our fishes reproduce in our aquariums, it's a pretty amazing achievement, really. Think about it: An animal is comfortable enough in the environment which you have provided, and healthy enough under your care to engage in eons-old reproductive activity, just like occurs in Nature. Now, sure, with some fishes, like many livebearers, this reproductive behavior is almost inevitable in captivity. It's still amazing to see, though isn't it?

And of course, there are some fishes, like Discus, for which spawning is not considered "inevitable." These fishes require very specific environmental conditions, social hierarchies, and time, in order for this to occur. It's not "impossible"- just a bit more demanding of us...
What is it about some fishes which challenges us to make them spawn? Is it some sort of environmental  "trigger" that is required? Or is it simply something in the "genetic programming" of the fish, which has a "timing mechanisms: which needs to be "unlocked" or something?

As a kid, I remember that the idea of breeding my fishes seemed so exotic; so aspirational...and often, unachievable.

Sometimes, it still feels that way, especially with some fishes.

I mean, sure, I was able to breed livebearers, killies, Kribs, Zebra Danios, Apistos, Cherry Barbs- fishes like that. Sometimes, these were the result of random chance, coincidences, or just plain old luck. Usually, my deliberately organized breeding attempts just sort of came up short all the time.

I mean, I'd have some success.

I had various Tetras breed when I intentionally tried to do it. However, for the most part, my "career" as a deliberate fish breeder has been essentially lacking. For whatever reason, I just don't have that combination of skill, desire, and a certain kind of patience that almost every talented fish breeder seems to possess in abundance.

The combination which leads to success with so many types of fishes.

And, that's okay. I made peace with that a long time ago. Thank goodness there are so many hobbyists out there who have that skill set and desire! Where would the hobby be without you guys?

Yeah, not everyone has the right combination of skill, patience, and resources to be a great fish breeder. Some of us just don't get bitten with that bug. I mean, the occasional random, spontaneous event happens, and we rejoice, panic, and hopefully learn from it!

Over the decades, I've had a surprisingly large number of those "spontaneous" spawning events with my fishes. You know, you wake up one morning and your Pencilfishes are acting weird...Next thing you know, there are clouds of eggs flying all over the tank...

That sort of stuff.

And after the initial surprise and excitement, during my "postgame analysis", I'd always try to figure out what led to the spawning event...It was usually pure luck, coupled with providing the fishes a good environment, rather than some intentionally-spawning-focused efforts I made.

And after a few years of experiencing this sort of thing, I began to draw the conclusion that it was the result of going out of my way to focus on recreating the correct environmental conditions for my fishes on a full-time basis- not just for spawning- which led to these events occurring repeatedly over the years.

With all sorts of fishes, too.

When it happened again, a couple of years ago, in my experimental leaf-litter only tank, hosting about 20 Paracheirodon simulans ("Green Neon Tetras"), I came the conclusion, in a rather circuitous sort of way, that I AM a "fish breeder" of sorts.

Or, more precisely, a "fish natural habitat replication specialist."

A nice way of saying that by focusing on the overall environmental conditions of the aquarium on a full time basis, I could encourage more natural behaviors- including spawning- among the fishes under my care.

Of course, there is more to being a "successful" breeder than just having the fishes spawn. You have to rear the resulting fry, right? Sure, half the battle is just getting the fishes to lay eggs in the first place- a conformation that you're doing something right to make them comfortable enough to want to reproduce! And there is a skill set needed to rear the fry, too.

Yet, I think that with a more intensive and creative approach, our botanical-style aquariums can help with the "rearing aspect", too. Sure, it's more "hands-off" than the traditional "keep-the-fry-knee-deep-in-food-at-all-times" approach that serious breeders employ...but my less deliberate, more "hands-off" approach can work. I've seen it happen many times in my "non-breeding" tanks.

We're seeing more and more reports of "spontaneous" spawnings of all sorts of different fishes associated with blackwater conditions.

Often, it's a group of fishes that the aquarist had for a while, perhaps with little effort put into spawning them, and then it just sort of "happened." For others, it is perhaps expected- maybe the ultimate goal as it relates to a specific species...but was just taking a long time to come to fruition.

The "common denominator" in all of the reports we receive are that the fishes are displaying better overall color, vigor, and overall health after being recently exposed to the more "physiologically appropriate" conditions of a blackwater aquarium. Now, this is by no means us stating that blackwater/botanical-style tanks are somehow "magical", and possess the ability to make every fish automatically thrive and spawn- or that this is some amazing "secret" that we've stumbled upon.

Nope. It's as old as the hobby itself. It's hardly magic.

It's the work of Nature.

Rather, it's more of an affirmation of a theory which I've developed over the decades that fishes from "specialized environmental conditions"- even those which might be many generations captive-bred, can always benefit from being "re-patriated" to the conditions under which they have evolved for eons.

I often wonder what is wrong with the idea of a permanent setup- a setup in which the fishes are provided a natural setting, and left to their own devices to "do their thing..."

This is pretty much the "classic" way many of us "bred" livebearers, killifish, and Rainbowfishes for a long time. It's a very low-labor, aesthetically interesting way to keep and breed these guys.

Now, I realize that a lot of hardcore, very experienced breeders will scoff at this- and probably rightly so. For the serious breeder, giving up control when the specific goal is the reproduction of your fishes is probably not a good thing. Practicality becomes important- hence the employment of clay flowerpots, spawning cones, breeding traps, bare tanks to raise fry, etc.

Sure, to a fish, a cave is a cave, be it constructed of ceramic or if it's the inside of a hollowed-out Cariniana pod. To the fish, it's a necessary place to spawn quietly and provide a defensible territory to protect the resulting fry.

In all likelihood, they couldn't care less what it is made of, right? And to the serious or professional breeder, viable spawns are the game.

And rearing the fry is the whole game!

No discussion of rearing our little fishes would be complete without revisiting the idea of a botanical-influenced "nursery" tank for fishes. You know where I'm going with this, right?

I think it's interesting for a number of reasons:

First, as we've discussed many times, the humic substances and other compounds associated with leaves and other botanicals, when released into the water, are known to have beneficial health impact on fishes. The potential for antimicrobial and antifungal effects is documented by science and is quite real.

Wouldn't this be something worth investigating from our unique angle? 

I think so!

Additionally, rearing young fishes in the type of environmental conditions under which they will spend the rest of their lives just makes a lot of sense to me. Having to acclimate young fishes into unfamiliar/different conditions, however beneficial they might be, still can be stressful to them.

So, why not be consistent with the environment from day one?

Wouldn't a "botanical-style fry-rearing system", with it's abundant decomposing leaves, biofilms, and microbial population, be of benefit?

I think so.

This is an interesting, in fact, fundamental aspect of botanical-style aquariums; we've discussed it many, many times here: The idea of "on board" food cultivation for fishes.

The breakdown and decomposition of various botanical materials provides a very natural supplemental source of food for young fishes, both directly (as in the case of fishes such as wood-eating catfishes, etc.), and indirectly, as they graze on algal growth, biofilms, fungi, and small crustaceans which inhabit the botanical "bed" in the aquarium.

And of course, decomposing leaves can stimulate a certain amount of microbial growth, with infusoria, forms of bacteria, and small crustaceans, becoming potential food sources for fry. I've read a few studies where phototrophic bacteria were added to the diet of larval fishes, producing measurably higher growth rates. Now, I'm not suggesting that your fry will gorge on beneficial bacteria "cultured" in situ in your blackwater nursery and grow exponentially faster.

However, I am suggesting that it might provide some beneficial supplemental nutrition at no cost to you!

It's essentially an "evolved" version of the "jungle tanks" I reared killies in when I was a teen. A different sort of look- and function! The so-called "permanent setup"- in which the adults and fry typically co-exist, with the fry finding food amongst the natural substrate and other materials present I the tank. Or, of course, you could remove the parents after breeding- the choice is yours.

While I believe that we can be lucky about having fishes spawn in our tanks when that wasn't the intent, I don't believe that fishes reproduce in our tanks solely  because of "luck." I mean, sure you will occasionally happen to have stumbled n the right combination of water temp, pH, current, light, or whatever- and BLAM! Spawning. However, I think it's more of a cumulative result of doing stuff right. For a while.

So, what is wrong with the idea of a permanent setup- a setup in which the fishes are provided a natural setting, and left to their own devices to "do their thing..?"

There really is nothing "wrong" with that. 

I guess my personal approach to fish breeding has always been, "If it happens, great...If not, I want the fishes to have an environment that mimics the one they're found in naturally." And that works to a certain extent, but I can see how many hobbyists feel that it's certainly not the practical way to do systematic, controlled breeding. 

Yet, isn't their something wonderful (for those of us who are not hell-bent on controlling the time and place of our fish's spawnings) to check out your tank one night and see a small clutch of Apisto fry under the watchful eye of the mother in a Sterculia pod or, a bunch of eggs of your fave Cory adorning the substrate, or whatever? Perhaps not as predictable or controllable as a more sterile breeding tank, but nonetheless, exciting!

It's about wonder. Awe. The happenstance of giving your fishes exactly what they need to react in the most natural way possible.

And that's pretty cool, isn't it?

Stay enthralled. Stay Excited. Stay diligent. Stay observant...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



May 13, 2021


So, really, what happens when a leaf falls into a stream?

There is amazing beauty and life to be found in what seems to be disorder and decay in aquatic systems. Yeah, decay and breakdown- processes which we have talked about extensively on these pages. It's a fantastic, dynamic process. Need an example of this dynamic?

Look no further than our friends, the leaves...You know, the plant materials that ecologists call allochthonous input- material imported into the aquatic ecosystem from outside it...Such as...fallen leaves.

The process which happens when a leaf falls into the water is an incredible example of the elegance of Nature and the dependency and interrelationship between terrestrial and aquatic habitats.

So...What makes leaves fall off the trees in the first place?

Well, it's simple- er, rather complex...but I suppose it's simple, too.😆

Essentially, the tree "commands" leaves to fall off the tree, by creating specialized cells which appear where the leaf stem of the leaves meet the branches. Known as "abscission" cells. If you're a word enthusiast, you'll love the little fact that they actually have the same Latin root as the word "scissors", which, of course, implies that these cells are designed to make a cut! 

And, in tropical species of trees, the process of leaf drop is vitally important to the surrounding environment.

The nutrients are typically bound up in the leaves, so a regular release of leaves by the trees helps replenish the minerals and nutrients which are typically depleted from eons of leaching into the surrounding forests. And the rapid nutrient depletion, by the way, is why it's not healthy to burn tropical forests- the release of nutrients as a result of fire is so rapid, that the habitat cannot process it, and in essence, the nutrients are lost forever.

Now, interestingly enough, most tropical forest trees are classified as "evergreens", and don't have a specific seasonal leaf drop like the "deciduous" trees than many of us are more familiar with do...Rather, they replace their leaves gradually throughout the year as the leaves age and subsequently fall off the trees.

The implication here?

There is a more-or-less continuous "supply" of leaves falling off into the jungles and waterways in these habitats, which is why you'll see leaves at varying stages of decomposition in tropical streams. It's also why leaf litter banks may be almost "permanent" structures within some of these bodies of water!

So, what is the fate of a leaf that falls into a jungle stream?

Almost immediately after it falls into the water and becomes submerged, the leaf leaches out some sugars and carbohydrates. These compounds tend to be dispersed widely into the water via current or other factors. Interestingly, studies have determined that when leaves enter the streams, their nitrogen content generally increases.

It's a by-product of respiration. This respiration is seen as evidence of microbial colonization on the leaf surfaces, which can be corroborated by the increase of oxygen consumption in the vicinity of the submerged leaf accumulation.

Leaves are surprisingly variable botanical structures, and they can vary compositionally significantly by species, and sometimes, within a species! Studies have shown that different leaves of the same species can contain up to a tenfold difference in difficult-to-digest tannins, with one leaf containing as little as 3 percent tannins and another leaf as much as 33 percent! This impacts the breakdown of the leaves and how quickly and easily they are assimilated into the aquatic environment.

Energy- in the form of organic carbon, nitrogen, and other nutrients- flows from the leaves into the waters, contributing significantly to these habitats. And among the most important roles of these nutrients in the aquatic habitats is to power the process of decomposition. And decomposition, in turn, is the process which powers the development of aquatic food webs.

In the decomposition process, the leaf's constituent elements follow multiple pathways, and as leaf litter is broken down into smaller and smaller particles, there are many opportunities for its elements to reenter the stream food web.

Of course, the physical leaf itself provides "fodder" for the fungi-those gooey "strings" you see whenever you add leaves to your aquarium. The fungi readily colonize the leaf surfaces. Stream-dwelling asexual fungi are called "Ingoldian hyphomycetes" by ecologists, in honor of the mycologist C.T. Ingold, who first described them in detail. These fungi supply much of the energy in stream ecosystems. 

They're really important!

How important?

Well, research by ecologists suggests that not only are fungi needed to start the initial break-down of leaves, but that fungi are the principle organisms involved in converting leaf materials to a more palatable form for other organisms. As the fungi work their biological magic, they facilitate the softening of the leaf, allowing our buddies, the bacteria ,to further break them down physically.

The mesophyll of the fungi produce enzymes that significantly degrade "structural polysaccharides", like cellulose, which results in a softening of the leaf structure which increases their food value for shredders. We call leaves which have been acted upon in this manner by aquatic fungi "conditioned" leaves.

Bacteria arrive on the scene to form part of what we call "biofilms", a complex community of algae, bacteria, fungi, and protozoans living in a matrix of secretions that adhere to the leaf surfaces themselves.

Biofilms form when bacteria adhere to surfaces in some form of watery environment and begin to excrete a slimy, gluelike substance, consisting of sugars and other substances, that can stick to all kinds of materials, such as- well- in our case, leaves. Biofilms continue the work started by fungi to soften the leaves for other organisms along this food chain, typically insects.

Usually, about 4-7 days, aquatic insects (typically "gnats") start to arrive on the scene, joining in on the bounty that the submerged leaf provides. These "grazers" are typically insects like caddisfly larvae, and even aquatic organisms like snails. They specialize in feeding off of the biofilms on the leaf surfaces with specialized mouthparts. Larger organisms, like various insect larvae and worms, shred the leaf with their tearing mouthparts.

Other aquatic insects are collectively known as "collector/gatherers." These insects move slowly along the stream bottom, searching for dead organisms, detritus, or other food particles.

Another group of organisms filter particles of biofilms or tiny bits of the leaves which are dislodged by grazers and shredders as they float downstream in the current. These filter feeding organisms may be either free-swimming or sessile (attaching to the leaf tissue) to feed and grow. They'll consume organic detritus and other materials in the water column as well. Some of these filter-feeding organisms, such as Hydra and amphipods are predators, too, opportunistically feeding on live organism which happen to float on by. 

Finally, some larger aquatic insects are actually predatory upon the other, smaller insects which feed on the bounty of leaf litter. They , in turn, form a part of the diet of the "alpha" species in these bodies of water- fishes.

Of course, fishes will take advantage of the leaves themselves, the fungi and bacterial biofilms which colonize them and soften them, as well as the various invertebrates and insects which break them down, and the resulting detritus which is produced as part of this decomposition process.

The largest proportion of allochthonous organic matter entering most streams comprises leaves, bark, and wood— notably, twigs.

The carbon and nitrogen contained within leave are assimilated and released at various stages of their decomposition process.

In each step of this aquatic food web, energy is transferred from one organism to another, and from one trophic (energy) level of the aquatic community to the next.

Thus, an entire aquatic food web is built around a community of fungi colonizing fallen leaves!

I come back to this concept again and again, because so many people who are new to the idea of botanical-style aquariums and our practice of adding botanical materials into our tanks simply ask, "Why?"

It makes perfect sense to ask this question. And it also makes perfect sense to be a bit hesitant about the idea of tossing in a bunch of leaves and seed pods and stuff into your "perfectly clean", well-maintained aquarium. We've been told for generations that we need to keep our tanks free from extraneous additions of organic materials. To many hobbyists, this is rightly viewed as adding "bioload" to the aquarium, which it is.

However, rather than just viewing the addition of leaves and such as a means to pollute your tank, I think it's more important to understand that the leaves are actually "fuel"- the power for the ecosystem which is our closed system aquarium.

It's absolutely fundamental to what we do.

Adding leaves to our aquariums is a functional re-creation of a natural process. It's important to note that the primary rationale within our movement for adding leaves to our tanks is not aesthetic.Sure, they do look cool- but that's a collateral benefit of their most beautiful attribute: The function and benefits which they bring.

Leaving these materials in situ to follow the process of softening, recruiting fungal growths, biofilms, and other organisms, and allowing them to completely break down is how we embrace the process of creating a functional closed aquatic ecosystem in our aquariums.

I've said this before, and I'll say it one more time (I can't say it often enough, really!):

A truly "natural" aquarium is not sterile. It encourages the accumulation of organic materials and other nutrients- not in excess, of course. Biofilms, fungi, algae...detritus...all have their place in the aquarium. Not as an excuse for lousy or lazy husbandry- NO- but as part of the 'microbiome", and to serve as supplemental food sources for the other life forms in our tanks.

Some of the decayed material is subsequently recycled as nutrients, like phosphorus (in the form of phosphate, PO4-3) and nitrogen (in the form of ammonium, NH4+) which are readily available for plant growth. Carbon is released largely as carbon dioxide that acts to lower the pH of the aquarium water.

We need to get over the "block" which has espoused a "sanitized" version of Nature. I hit on this theme again and again and again, because I feel like, globally, our community is like 75% "there"- almost entirely "bought in" to the idea of really naturally-appearing and functioning aquarium systems.

Understanding that stuff like the aforementioned decomposition of materials, and the appearance of biofilms- comprise both a natural and functional part of the microcosms we create in our tanks.

This is true in both the wild habitats and the aquarium, of course.

The same processes and function which govern what happens to these materials in the wild occur in our aquariums. And, if we reject our initial instinct to "edit" what Nature does, the aquarium takes on a look and vibrancy that only She can create.

Embrace, don't edit.

Leave the stuff in there until it decomposes.

It's a real mental shift that we as hobbyists have to make. Sure, there will always be a lot of people that don't like the look of brown water, decomposing leaves, biofilms and fungi in their aquariums. It's a radically different look than what we've come to accept an aquarium "should" look like for the better part of the century..

We have to accept Nature's input here. We can't be afraid of it. We need not be.

Nature dictates the speed by which this decomposition process occurs. Nature "recruits" the organisms which power our little ecosystems.

Yes, we "set the stage" for it- but Nature is in full control.

She always was, and always will be.

Our journey starts with a falling leaf. 

Leaves represent a true confluence of terrestrial and aquatic elements, working together to create a unique and inspiring aquatic habitat. By replicating, at least on some level, an "unedited" interpretation of the process which builds these habitats, we open up new possibilities, foster breakthroughs in aquatic husbandry, and further the state of the art of the aquarium hobby.

Yeah, it starts with a falling leaf...


Stay inquisitive. Stay studious. Stay observant. Stay persistent. Stay patient. Stay bold...

And Stay Wet.


Scott Fellman

Tannin Aquatics