March 22, 2021


Assumptions, variables, recommendations, and ideas...

The idea of utilizing botanicals in our aquariums to help create the ecology of the aquarium, as well as to impact its physical/chemical environment, is evolving rapidly. We are at that "phase" in our understanding where we are beginning to develop some best practices, experiment a bit more, question lots of stuff...and make the occasional assumption or two.

Or more.

For example, I've long had a theory that it might be beneficial to have several different types of botanical materials in your tank. Not for aesthetics mind, you, but for other reasons.

My theory goes something like this:

Most plant products contain some similar compounds, such as tannins, mic substances, minerals, etc. However, I believe that many contain varying qualities of these substances, and based on the structure/durability of the specific botanical item, are released into the water at different rates as the materials break down.

And of course, there are likely other variables that no doubt come into the equation, such as how a specific botanical was prepared. How dry it actually was before immersion, the conditions under which the mother plant the botanical came from was growing under, the time of year it was harvested, etc., etc., etc.

I mean, it's a assumption of sorts. 

However, I think it makes some sense, right?

I mean, botanists know that specific plants and their leaves contain varying amounts of tannins and other compounds. Especially, leaves. Think about it. Some leaves may have greater concentrations of these substances than others, and thusly, are potentially more "potent" for our purposes...right? And at different times of year, this can likely vary. And therefore, it could make using certain leaves more effective than others at different times.

Well, yeah, in theory, huh?

The reality of this is that we simply don't have all of the answers...or even all of the questions to ask to get the answers! We simply have to experiment.

We have to try stuff.

And, one could take it further with my theory and sort of speculate that, with the potential variations in (desired) compounds in various botanicals, that using a variety in one situation sort of covers a number of possibilities at once.

Since I started playing with leaves and such, years ago, I've always sort of acted upon a leap of faith; a theory about what exactly they do. And this sort of tempted my work with them over the years. When I initially started, I was a bit hesitant, scared, even, of somehow poisoning my fishes and "crashing" my tanks. 

However, it stood to reason that if some of these materials (leaves, seed pods, etc) are present in natural aquatics habitats around the world without killing fishes en masse, it would be perfectly okay to use them in an aquarium...right?

Well, yes. And no. 

I mean, many of the materials that we have are not the exact botanical items found in every steam or river around the world. They are representative in many cases- facsimiles of what is found in Nature. I mean, oak leaves are not found in Southeast Asia, right? 

However, they accomplish the same thing that an Astrocaryum or Ceiba leaf might in its native territory, right?

That's what I've theorized over the years...

And happily, it kind of worked out that way. As I experimented with more and more stuff, and saw very positive results with my fishes, I felt pretty confident that something beneficial was occurring as a result of adding this stuff to my aquariums!

There were, and continue to be- questions. And assumptions. Some which we simply have to make at this point, because we just don't have all of the information necessary to state with absolute certainty what is "correct."

Now, one could assume that the leaves and other parts of the plant which find their way into natural waters might contain varying combinations of certain compounds, thus releasing different amounts proportionally into the water...However,  the essential "function" of any given leaf or seed pod breaking down in water is the same around the world, right?

Probably...I mean, likely...right? I mean, they're all essential "constructed" of the same stuff, and posses many of the same compounds in their structures, like lignin, etc... perhaps the concentrations vary, or the presence of certain other substances could be different in different botanical materials, but...


And of course, there are other variables to consider.

I mean, in a natural water course, you typically have more water volume than the average home aquarium, and it's an open ecosystem, with inputs from and outputs to, the surrounding environment, creating dilution. An aquarium is a closed system, and input/export to and from the environment is largely dependent upon us (the fish geeks) to control. And of course, being closed systems, it's at least theoretically possible to "over-dose" our tanks with "stuff", isn't it?

Well, in terms of biological impact, at least. 

We need to allow the microorganisms and other creatures to multiply to sufficient populations to be able to handle the influx of new materials. Simple as that.

Our aquariums likely can biologically and chemically assimilate and process only so much material, right?  Sure. I mean, we've seen cases where over-zealous "tinters" have seen fishes gasping at the surface because they added too much stuff to their tanks too quickly, and the CO2 level rose rapidly as a result.

Yeah. Stuff like that. 

Although it's likely that the compounds present in the botanical materials are not sufficient in concentration and of themselves to do harm to fishes, the impact of adding them to our tanks is probably more "biological" in nature. In other words, they impact the biological capacity of the aquarium.

And that's likely how the "You need to use 'X' number of Catappa leaves per liter of water" recommendations that we hear of  came about.

Trial and error...and (hopefully) conservative experiments.

I mean, I hate "rules" like that, specifically for natural materials which no doubt have varying levels of the compounds that we're interested in, based on so many possible factors...But it's a starting point, I guess.

Until a sophisticated scientific assay of every leaf, every seed pod, and every type of wood that we utilize in aquariums is completed, determining average concentrations of _________ In a given sample size, "dosing" recommendations are just that...Recommendations.





A starting point.

And that's okay, because this is a hobby. An art as much as it is a science.

Of course, the big idea is not to assume too much. 

Rather, it's to research, experiment. Test, evaluate. Observe. Adjust. Rinse and repeat.

Sometimes, it's okay to assume...

Just not too much!

Today's little lesson in putting things into perspective in our tinted world.

Stay curious. Stay analytical. Stay fascinated. Stay focused...

And Stay Wet.


Scott Fellman

Tannin Aquatics

My Fave fish for botanical-style aquariums: Some long-overdue thoughts- Part 1 of many?

Of all of the topics we cover here in "The Tint", the one we discuss the least (rather shockingly, I might add) is the fishes that we keep in our tanks! Yeahs, I talk more about fungi, sediments, decomposition, and leaf litter than I do about fishes...

And of course, when someone hit me up the other day and asked, "Scott, what are your favorite fishes for botanical-style aquariums?" I was like, "Well, shit- I never even covered that!" I mean, we should have covered that before. It's a cool topic. I'm kind of unsure why, actually.

Probably because most of the articles on this topic are kind of...oh, crap, I'll say it- just boring. Ever read one of those "Top 10" listicle thingys about fishes? They usually-well, suck. Harsh, but they're kind of boring, IMHO. I mean, they talk about the size of the fish, what it eats, and what size tank you can keep it in. I mean, helpful, but..I dunno. Boring. Stuff you can pretty much find in any aquarium-related reference. You don't come here for that, I hope... So, we'll try to cover these fishes from "a slightly different perspective", as I like to say.

So, let's hit that topic today! Okay, let's hit some of it list is longer than my patience to discuss them all in one piece! And I'll try my best not to do it the boring way...

Oh, damn, I might have a bunch of fishes...but I don't think I'm gonna cover all of them today...

Give me a break- it's a start, right?

Now, here's the thing- you'll find that my fish choices are as much based upon  the habitats that they come from as they are about the fishes themselves..

Okay, so let's get this party started...

In no particular order ( well, maybe in a sort of order..):

Sailfin Characin (Crenuchus spilurus)

We've all had that ONE fish which just sort of occupies a place in our hearts and minds- a fish that-for whatever reason- bites you and never lets go, right? I think that every serious aquarist has at least one such a fish..

Here's mine...

Of course, it's also about the habitat which this fish lives in that's kept me under its spell for so long...

As a lover of leaf-litter in our natural, botanical-style aquariums, I am fascinated not only by this unique ecological niche, but by the organisms which inhabit it. I've went on and on and spoken at length about many of the microorganisms, fungi, insects, and crustaceans which add to the diversity of this environment. And of course, we've looked at some of the fishes which live there, too! Perhaps not enough, actually...

One of my all-time favorite fishes- and my absolute favorite characin is none other than the amazing "Sailfin Tetra", Crenuchus spilurus!  This is a truly awesome fish- not only is it attractive and morphologically cool-looking, it has a great demeanor and behaviors which separate it from almost every other characin out there! 

I first fell for this fish as a kid, when I saw a cool pic of it in my dad's well-worn copy of William T. Innes' classic book, Exotic Aquarium Fishes. The book that pretty much assured me from toddler days that I'd be a fish geek. I obsessed over the book before I could even read...

I was hooked from the start with Crenuchus, especially when reading about the romantic etymology of the name!  And it just seemed so "mysterious" and unattainable, even in the 1930's...well, especially back in the 1930's, but it seemed downright exotic! To this day, it's one you just don't see too much of in the hobby. And then, tying it together with my love of those leaf-litter-strewn habitats, it was a combo which I couldn't resist!

I never got this fish out of my system, and it took me like 30-plus years of being a fish geek to find this fish in real life. And, you know that I jumped at the chance..It was so worth the wait!

It's almost "cichlid-like" in behavior: Intelligent, interactive, and endearing. It has social behaviors which will entertain and fascinate those who are fortunate enough to keep it.

Now, I admit, it's definitely NOT the most colorful characin on the planet. But there is more than this fish than meets the eye.

It all starts with its most intriguing name...

The Latin root of the genus Crenuchus means "Guardian of The Spring"- a really cool, even romantic-sounding name which evokes imagery-and questions! Does it mean the "protector" of a body of water, or some honorary homage to everyone's favorite season? Not sure, but you must agree that the name is pretty cool! In greek, it's krenoychos -"The God of running waters."

Yeah. That's the shit. I mean, do Latin names get any cooler than that?

The Crenuchidae (South American Darters) is a really interesting family of fishes, and includes 93 species in 12 genera throughout the Amazon region. Most crenuchids are- well, how do we put it delicately- "chromatically challenged" ( ie; grey-black-brown) fishes, which tend to lie in wait near the substrate (typically leaf litter or aggregations of branches), feeding on insects and micro invertebrates. And the genus Crenuchus consists of just one species, our pal Crenuchus spilurus, a fish which shares habits and a body shape that are more commonly associated with Cyprinids and...cichlids!

That's just weird.

Now, the relatively subdued coloration serves a purpose, of course. These fishes live among leaf litter, root tangles, and botanical tinted water...which demand (if you don't want to be food for bigger fishes and birds) some ability to camouflage yourself effectively. 

The Sailfin is an exception to the "drab" thing, and it's remarkably attractive for a very "simple" benthic-living fish. Sure, on the surface, it's not the most exciting fish out there, especially when it's a juvenile...but it's a fish that you need to be patient with; a fish to search for, collect, hold onto, and enjoy as it matures and grows. As the fish matures, in true "ugly duckling"🐥  style, it literally "blossoms" into a far more attractive fish.

The males have an extended dorsal and anal fin, and are larger and more colorful than females. Yes, colorful is relative here, but when you see a group- you'll notice the sexual dimorphism right away, even among juveniles.

Individuals spend a lot of their time sheltered under dead leaves, branches, roots, and aquatic plants. They tend to "hover", and don't dart about like your typical Tetra would. In fact, their behavior reminds me of the Dartfishes of the marine aquarium world...They sort of sit and flick their fins, often moving in slow, deliberate motions. Communication? Perhaps.

The Sailfin feeds during the daylight hours, and spends much of its day sheltering under branches, leaves, and root tangles, and is a mid-water feeder, consuming particulate organic matter, such as aquatic invertebrates, insects, bits of flowers, and fruits- the cool food items from outside of the aquatic environment that form what ecologists call allochthonous input-materials from outside of the aquatic habitat, which are abundant in the terrestrial habitats surrounding the aquatic ones which we love to model our aquariums after.

Tucano Tetra (Tucanoichthys tucano)

You all know by now that my philosophy is to study and understand the environments from which our fishes come, and to replicate them in function and form as best as possible. It doesn't always mean exactly- but it's definitely NOT forcing them to adapt to our "local tap water "conditions without any attempt to modify them.

I have a very current  "case study" of my own that sort of reflects the execution of my philosophy.

As many of you know, I've had a long obsession with the idea of root tangles and submerged accumulations of leaves, branches, and seed pods. I love the silty, sedimented substrates and the intricate interplay of terrestrial plant roots with the aquatic environment.

I was doing a geeky "deep dive" into this type of habitat in Amazonia one evening, and stumbled upon this gem from a scientific paper by J. Gery and U. Romer in 1997:

"The brook, 80-200cm wide, 50-100 cm deep near the end of the dry season (the level was still dropping at the rate of 20cm a day), runs rather swiftly in a dense forest, with Ficus trees and Leopoldina the water as dominant plants. Dead wood. mostly prickly trunks of palms, are lying in the water, usually covered with Ficus leaves, which also cover the bottom with a layer 50-100cm thick. No submerse plants. Only the branches and roots of emerge plants provide shelter for aquatic organisms.

The following data were gathered by the Junior author Feb 21, 1994 at 11:00AM: Clear with blackwater influence, extremely acid. Current 0.5-1 mv/sec. Temp.: Air 29C, water 24C at more than 50cm depth... The fish fauna seems quite poor in species. Only 6 species were collected I the brook, including Tucanoichthys tucano: Two cichlids, Nannacara adoketa, and Crenicichla sp., one catfish, a doradid Amblydoras sp.; and an as yet unidentified Rivulus, abundant; the only other characoid, probably syncopic, was Poecilocharax weitzmani."

Yeah, it turned out to be the ichthyological description of the little "Tucano Tetra", Tucanoichthys tucano, and was a treasure trove of data on both the fish and its habitat. I was taken by the decidedly "aquarium reproducible" characteristics of the habitat, both in terms of its physical size and its structure. 

Boom! I was hooked.

I needed to replicate this habitat! And how could I not love this little fish? I even had a little aquarium that I had been dying to work with for a while. 

It must have been "ordained" by the universe, right?

Now, I admit, I wasn't interested in, or able to safely lower the pH down to 4.3 ( which was one of the readings taken at the locale), and hold it there, but I could get the "low sixes" nailed easily! Sure, one could  logically call me a sort of hypocrite, because I'm immediately conceding that I won't do 4.3, and I suppose that could be warranted...

However, there is a far cry between creating 6.2pH for my tank, which is easy to obtain and maintain for me, and "force-fitting" fishes to adapt to our 8.4pH Los Angeles tap water! 

And of course, with me essentially trashing the idea of executing a hardcore 100% replication of such a specific locale, the idea was essentially to mimic the appearance and function of such an igarape habitat, replete with lots of roots and leaf litter.

And the idea of executing it in a nano-sized aquarium made the entire project more immediately attainable and a bit less daunting. I wanted to see if I could pull off a compelling biotope-inspired aquairum on a small scale.

That's where my real interest was.

So, even the "create the proper conditions for the fish instead of forcing them to adapt to what's easiest for us" philosophy can be nuanced! And it should! I don't want to mess with strong acids at this time. It's doable...a number of hobbyists have successfully.  However, for the purposes of my experiment, I decided to happily abstain for now, lol.

And without flogging a dead horse, as the horrible expression goes, I think I nailed many of the physical attributes of the habitat of this fish. By utilizing natural materials, such as roots, which are representative of those found in the fish's habitat, as well as the use of Ficus and other small leaves as the "litter" in the tank, I think we created a cool biotope-inspired display for these little guys!

And man, I love this tank!

Being able to pull off many aspects of the look, feel and function of the natural habitat of the fish was a really rewarding experience. A real "case study" for my philosophy of fish selection and stocking.  

Green Neon Tetra (Paracheirodon simulans)

Everyone knows the Neon Tetra, Paracheirodon inessi. It's a strong candidate for the title of "Official fish of the Aquarium Hobby!" Of course, there other members of the genus Paracheirodon which hobbyists have become enamored with, such as the diminutive, yet equally alluring P. simulans, the "Green Neon Tetra." Topping out at around 3/4" (about 2cm) in length, it's certainly deserving of the hobby label of "nano fish!"

You can keep these little guys in nice -sized aggregations..I wouldn't necessarily call them "schools", because, as our friend Ivan Mikolji beautifully observes, "In an aquarium P. simulans seem to be all over the place, each one going wherever it pleases and turning greener than when they are in the wild."


This cool little fish is one of my fave of what I call "Petit Tetras." Hailing from remote regions in the Upper Rio Negro and Orinoco regions of Brazil and Colombia, this fish is a real showstopper! According to ichthyologist Jacques Gery, the type locality of this fish is the Rio Jufaris, a small tributary of the Rio Negro in Amazonas State.

One of the rather cool highlights of this fish is that it is found exclusively in blackwater habitats. Specifically, they are known to occur in  habitats called "Palm Swamps"( locally known as "campos") in the middle Rio Negro. These are pretty cool shallow water environments! Interestingly, P. simulans doesn't migrate out of these shallow water habitats (less romantically called "woody herbaceous campinas" by aquatic ecologists) like the Neon Tetra (P. axelrodi) does. It stays to these habitats for its entire lifespan.

These "campo" habitats are essentially large depressions which do not drain easily because of the elevated water table and the presence of a soil structure, created by our fave soil, hydromorphic podzol! "Hydromorphic" refers to s soil having characteristics that are developed when there is excess water present all or part of the time. 

(Image by G. Durigan)

So, if you really want to get hardcore about recreating this habitat, you'd use immersion-tolerant terrestrial plants, such as Spathanthus unilateralis, Everardia montana, Scleria microcarpa, and small patches of shrubs such as Macairea viscosa, Tococa sp. and Macrosamanea simabifoli. And grasses, like Trachypogon. 

Of course, our fave palm,  Mauritia flexuosa and its common companion, Bactris campestris round out the native vegetation. Now, the big question is, can you find any of these plants? Perhaps...More likely, you could find substitutes. 

Just Google that shit! Tons to learn about those plants!

These habitats are typically choked with roots and plant parts, and the bottom is covered with leaves and fallen palm fronds...This is right up our alley, right?

Of course, if you really want to be a full-on "baller" and replicate the natural habitat of these fishes as accurately as possible, it helps to have some information to go on! So, here are the environmental parameters from these "campo" habitats based on a couple of studies I found:

The dissolved oxygen levels average around 2.1 mg/l, and a pH ranging from 4.7-4.3. KH values are typically less than 20mg/L, and the GH generally less than 10mg/L. The conductivity is pretty low. 

The water depth in these habitats, based on one study I encountered, ranged from as shallow as about 6 inches (15cm) to about 27 inches (67cm) on the deeper range. The average depth in the study was about 15" (38cm). This is pretty cool for us hobbyists, right? Shallow! I mean, we can utilize all sorts of aquariums and accurately recreate the depth of the habitats which P. simulans comes from!

We often read in aquarium literature that P. simulans needs fairly high water temperatures, and the field studies I found for this fish this  confirm this.

Average daily minimum water temperature of P. simulans habitats in the middle Rio Negro was about 79.7 F (26.5 C) between September and February (the end of the rainy season and part of the dry season). The average daily maximum water temperature during the same period averaged about 81 degrees F (27.7 C). Temperatures as low as 76 degrees' (24.6 C) and as high as 95 degrees F (35.2 C) were tolerated by P. simulans with no mortality noted by the researchers.

Bottom line, you biotope purists? Keep the temperature between 79-81 degrees F (approx. 26 C-27C).

Researchers have postulated that a thermal tolerance to high water temperatures may have developed in P. simulans as these shallow "campos" became its only real aquatic habitat.

The fish preys upon that beloved catchall of "micro crustaceans" and insect larvae as its exclusive diet. Specifically, small aquatic annelids, such as larvae of Chironomidae (hey, that's the "Blood Worm!") which are also found among the substratum, the leaves and branches. 

Now, if you're wondering what would be good foods to represent this fish's natural diet, you can't go wrong with stuff like Daphnia and other copepods. Small stuff makes the most sense, because of the small size of the fish and its mouthparts.


This fish would be a great candidate for an "Urban Igapo" style aquarium, in which rich soil, reminiscent of the podzols found in this habitat is use, along with terrestrial vegetation. You could do a pretty accurate representation of this habitat utilizing these techniques and substrates, and simply forgoing the wet/dry "seasonal cycles" in your management of the system.

There are a lot of possibilities here. 

One of the most enjoyable and effective approaches I've taken to keeping this fish was a "leaf litter only" system (which we've written about extensively here. Not only did it provide many of the characteristics of the wild habitat (leaves, warm water temperatures, minimal water movement, and soft, acidic water).

As you may recall, I utilized that particular setup as a "test bed" for my "internal food production" theory- not adding any supplemental food to the tank, and the little P. simulans simply thrived. They were active, colorful, and fat- which is a big "stretch" for a little fish! And there were two distinct spawning events in this tank!


So, maybe you've noticed a pattern to my love of certain much is based upon the habitats that they come from. My love for the fishes was amplified when I studied and learned more about the unique habitats from which each of these fishes come. The idea of recreating various aspects of the habitat as the basis for working with these fishes is irresistible to me!

Diptail or Brown Pencilfish (Nanostomus eques

This one really should have been the top choice if I were doing it in order. I LOVE everything about this fish. Well, almost everything.

Honestly, if a fish could earn the moniker "cool", this little guy would be it. It's absolutely not an overstatement to declare that these Pencilfishes have distinct personalities! They're not "mindless-drone, stupid schooling fishes", like some of the Tetras. (Sorry, my homies...Love ya' lots, but alas- you have no individual personalities...😂)

They are proud members of the family family Lebiasinidae. It was first described in 1876 by the legendary ichthyologist, Franz Steindachner. In fact, it was one of the first members of the genus Nanostomus to be discovered and described by science.

Cool, but that's not my main reason for loving this fish. There's a bunch of unique aspects to this fish's behavior which I find enormously compelling.

The Latin name of the species, eques, means "knight", "horseman", or "rider", in reference to this species’ unique oblique swimming angle. 

Ah, that "oblique swimming angle" thing. Yeah, they swim at an angle of about 45 degrees facing upwards. This angle is thought to give them an advantage in feeding. They see insects and such that fall from overhanging vegetation better than their horizontally-oriented buddies do. They get more food that way. Simple.

(Image by Fajoe, used under CC BY-SA 3.0) 

What I really love about these fish is that they are incredibly curious and obviously intelligent, checking out just about anything which goes on in their aquarium. You get the feeling when observing them that they are acutely aware of their surroundings, and once acclimated, are pretty much fearless. A fellow hobbyist once told me she thinks they're the freshwater equivalent of Pipefish...and that sounds about right..I agree with that 100%!

They're sociable, incredibly "chill" fish. Now, the thing about their ability to adeptly feed on allochthonous input into the aquatic environment makes them easy to feed. And it also gives you some clues as to the habitats they come from. Places where the food comes from the surrounding terrestrial environment. 

Foods from the surrounding environment, such as flowers, fruits, terrestrial insects, etc. These are extremely important foods for many fish species that live in these habitats. We mimic this process when we feed our fishes prepared foods, as stuff literally "rains from the sky!" Now, I think that what we feed to our fishes directly in this fashion is equally as important as how it's fed.

The environments which provide this food abundance also provide lots of opportunities to replicate in our aquariums. I love that about this fish. They come from really cool, really inspiring habitats.

They are also really adept at picking on epiphytic materials in their botanical-style aquariums. It's an observation I've made many times with these fish.

Yeah, they seem to spend a large amount of time picking at biofilm and other material adhering to botanicals, and specifically, wood. They engage in this activity almost constantly throughout the day (between feedings, of course!). I am convinced that they are likely not specifically targeting the biofilm directly; rather, I think that they're looking for tiny crustaceans and other life forms that live in the matrix.

Nonetheless, their picking distrubs the films and puts it into suspension, where it can more easily be removed by filtration. This was an unexpected "plus" of this most beloved group of fishes. Now, I must warn you, biofilm haters- you shouldn't even consider Pencilfishes as a biofilm "control mechanism", but I suppose that to you heathens, the "collateral benefit" is nice.

They are very aware, very adept feeders...Always ready to pounce. 

What's the thing I don't like about these fish?

Oh, they can be a bit skittish. Like, chill as they are, "stuff" just freaks them out.

They will, for seemingly no reason, launch themselves out of your open-top aquarium (well, those are the only types I keep...) with tremendous agility-sometimes landing a few inches away in the tank...Other times, completely leaving the tank, and well- usually this results in a very dried-out Pencilfish!

I guess the oblique swimming angle facilitates them reaching "escape velocity" rapidly. You get the feeling that they're always in "standby for launch!" mode. Like, full-on "defcon-5" mode.

Maybe, because they're always looking UP- the slightest disturbance from BELOW triggers a launch. I don't know, but it's as good a theory as any. And a 3-inch launch gets you away from a potential predator. A 6-inch launch lands you on the floor... Damn, a good adaptation for protection, this "launching" thing. But, like, who really wants to eat a Pencilfish, right? I guess the Pencilfish don't know that...They just jump. Millenia of genetic programming can't be overcome easily!

It sucks, but it's the downside to keeping them in open-top tanks. Lots of twisted branches and even floating plants DO help limit some of this "carpet surfing" behavior, but it's not a 100% perfect solution. I admit, These guys have, in the past played a central role in some of those "And then there were none" disappearing fish sagas that I've experienced over the years.

So, if you can keep them in a low- traffic area, employ lots of branches, and maybe some floating plants...maybe you'll avoid this.

I mean, these methods also occasionally work with Hatchetfishes...another fave of mine, but almost too suicidal, even for me. And that's why they are not in my top 10 list, if you're wondering..

Okay, I could probably do a top 10, or even a dozen- fave fishes, but I'd be writing all day on this topic. Honorable mention- The Checkerboard Cichlid (Dicrossus filamentosus)... My "go-to" cichlid for botanical-style tanks...I love them- even over Apistos...And, as one of my friends told me, "Of course you do Scott- they're fucking brown!" 

Damn, my friends really know me well, huh?

Just try them in your next botanical-style aquarium. You won't regret it.  Maybe we'll deep dive in the "Fellman style" on these guys next time...

Okay that's a start... I think I can safely employ the great line used by one of the aquarium hobby's great saltwater fish experts, Scott Michael, who, upon discussing such-and-such a fish would simply declare in a deadpan manner, "If you don't keep these fish, you're stupid.." 

How can you argue with THAT kind of assertion? I totally relate to that. Well, shit- you asked me what my faves knew I'd have some strong feelings about them, huh? 😆

Anyhow, I hope this little start gives you a look into the unorthodox way I think about the fish I select for my aquariums: So much of it is about studying a habitat I love, and then researching what fishes are found in it- and why. Then, creating the habitat for them. Like, "habitat-first."  Totally works for me.

I hope it works for you too!

Until Next time...

Stay thoughtful. Stay curious. Stay bold. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 





March 17, 2021


igapo ›   setup ›   substrate ›   urban igapo ›  

New start. New approach.

One of the best things about not having a lot of tanks in operation at the moment (Wait, let's correct that...the ONLY good thing about not having a lot of tanks in operation at the moment...😆) is that it gives you the opportunity to plan, review, and plot your next moves. 

I'm in such a phase at home, with my house undergoing a substantial remodel and all of my "full-size" tanks in storage for a couple more months. As I've told you previously, it's given me the opportunity to play with a lot of ideas quickly in "nano-sized" aquariums. 

And of course, I've thought s lot about how I'm going to start up my next botanical-style tanks.

Here's an approach I'm trying on one of them. I call it the "transitional" approach.

Okay, we've tackled our "Urban Igapo" idea a bunch of times here, with the technique being described and studied quite a bit. Now, the repetition of wet and dry "seasonal cycles" in the aquarium, although fascinating and the most novel takeaway from this approach, is but one way to apply the idea of evolving a "dry forest floor" into an aquatic habitat.

This is one of the most incredible and fascinating ecological dynamics in Nature, and it's something that we as a hobby have not attempted to model to any extent, until we started messing around with the idea of replicating it around 2017. Again, we're not talking about replicating the 'look" of a flooded forest after it's been flooded...That has been done for years by hobbyists, particularly in biotope design contests. An "aquascaping" thing. 

This is a bit different. 

We're talking about actually replicating and flooding the damn forest floor! Replicating the cycle of inundation. It's a functional approach, requiring understanding, research, and patience to execute. And the aesthetics...They will follow, resembling what you see in Nature. But the primary reason is NOT for aesthetics... 


So, the way this would work is to simply set up the tank like our "standard" approach to creating an "Urban Igapo"- utilizing a sedimented substrate (um, yeah, we make one....) to create a "forest floor." And then, you add leaves, botanicals, and perhaps, some terrestrial grass seeds, and even riparian plants.

You'd set whatever "hardscape" you want- driftwood, etc. in place. Of course, you'd have to water your little forest floor for some period of time, allowing the vegetation to sprout and grow. Based on the many times of played with the "Igapo" idea, this process typically takes around 2-3 months to establish the growth well. 

And then what? Well, you'd flood it!

You could do this all at one time, or over the course of several  days, depending upon your preference. I mean, you've waited a couple of months to add water to your tank...what's another few days? 😆 Now, sure, there's a difference between a 5-gallon tank and a 50- gallon tank, and it takes a lot longer to fill, so it's up to you how you want to approach this!

And what you'd initially end up with is a murky, tinted environment, with little bits of leaves, botanicals, and soil floating about. Sounds like a blast, huh? And when you think about it, this is not all that different, at least procedurally, from the "dry start" approach to a planted tank...except we're not talking about a planted tsmnk here.. I mean, you could do aquatic plants...but it's more of a "wholistic biome" approach...


The interesting thing about this approach is that you will see a tank which "cycles" extremely quickly, in my experience. In fact, Iv'e done many iterations of "Urban Igapo" tanks where there was no detectible "cycle" in the traditional sense. I don't have an explanation for this, except to postulate that the abundance of bacterial and microorganism growth, and other life forms, like fungal growths, etc., powered by the nutrients available to them in the established terrestrial substrate expedites this process dramatically.


That's my theory, of course, and I could be way, way off base, but it is based on my experience and that of others in our community over the past several years. I mean, there is a nitrogen cycle occurring in the dry substrate, so when it's inundated, do the bacteria make the transition, or do they perish, followed by the very rapid colonization by other species, or..?


An underwater biome is created immediately with this approach. Doing this type of "transition" is going to not only create a different sort of underwater biodiversity, it will have the "collateral benefit" of creating a very different aesthetic as well. And yeah, it's an aesthetic that will be dictated by Nature, and will encompass all of those things that we know and love- biofilms, fungal growth, decomposition, etc.


I've done this in aquariums up to 10 gallons so far, with great success, so I'm completely convinced that this process can be "scaled up" easily. The technique is the same. 

Now, one fundamental difference between this approach and the more "traditional" "Urban Igapo" approach is that it's a "one way trip"- start our dry and take it to "wet", without going through repetitive dry cycles. The interesting thing to me about this approach is that you're going to have a very nutrient-rich aquarium habitat, with a big diversity of life from the start. 

Could you plant aquatic plants in the substrate? Well, sure. You could use them from the start, or you could add them later on, if you wish. If you're using one of our sedimented substrates, you will be able grow many aquatic plants. 
I suppose the big question- the overarching curiosity that many of you have about this idea is why you'd try it. And the best answer that I can provide is...because it's a fascinating exercise in patience, experimentation, and fostering biodiversity. It will familiarize you with the influence of the terrestrial habitat and the dynamic which exists between the aquatic and the terrestrial habitat during seasonal changes. 
It's about process, and transition...And there is so much to learn here. 

It's still early days.


There is so much to learn and experiment with. Every single one of us, when we embark on a botanical-style aquarium adventure- is playing a key role in contributing to the "state of the art" of the aquarium hobby! Everycontribution is important...

Enjoy the process! 

Stay curious. Stay observant. Stay experimental. Stay bold...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

March 16, 2021


Getting to the bottom of the "sedimented substrate thing..."

Okay, today is one of those posts where I simply can't make any excuses for it being a bit blatantly commercial. And that's something that I have to live with, right? I mean, I own a company which sells natural materials for aquariums, and I have written a blog for over 5 years, and recorded a podcast for almost 2 yrs...every once in a while, a blog or podcast can focus on one of our products...and today is such a day!


Recently, we introduced a line of substrates called NatureBase. And, they've proven crazy popular! Yet, they generate a lot of questions...


We describe our products as "sedimented substrates", because that's what they are- consisting largely of clays, sand, soil, and other materials (mineral sediments!) which mimic some of the properties of the soils of South America and other locales that we find so compelling.

Now, one of the first questions people ask about our soils is "What makes them different than the other materials on the market?" Well, I could go on and on, but quite simply, the answer is that these substrates were formulated to replicate the terrestrial soils of these habitats, which become inundated during seasonal rains and flooding.

Forest floor soils in tropical areas are known by soil geologists as "oxisols", and have varying amounts of clay, sediments, minerals like quartz and silica, and various types of organic matter. So it makes sense that when flooded, these "ingredients" will have significant impact on the aquatic environment. This "recipe" is not only compositionally different than typical "off-the-shelf" aquarium sands and substrates- it looks and functions differently, too.

They weren't designed from the get go to replicate say, river, stream, or lake substrates writ large.

And, they weren't intended to be a "go-to" substrate to replace the standard commercial aquarium substrates, because: a) they're hand-mixed, and therefore more expensive, b) they're not specifically "aesthetic enhancements", c) they are not formulated to be general aquatic plant substrates d) because of their composition, they'll add some turbidity and tint to the aquarium water, at least initially (not everyone could handle THAT!)

Rather, the intention was that our first releases "Varzea" and "Igapo" were formulated to be "transitional" substrate materials- starting out as terrestrial, able to grow some grasses and plants, and eventually becoming saturated and ultimately, submerged, transitioning to a fully "aquatic" substrate material.


Perfect for use in our "Urban Igapo" simulations, which is exactly what we developed them know, the classic case of "scratching your own itch!"

Of course, this begs the question, "Can't they just be used like 'conventional' aquarium substrates from the start?"

And the answer is, "Yeah, they could. However, what will happen, because of their ingredients, is that they will create cloudy, turbid water in your aquairum." There is a reason why materials like fine clays and mineral sediments haven't been particularly popular ingredients in aquarium substrates before!

Some of the materials will not saturate immediately causing this turbidity for several days or more. Ultimately, however, the materials will settle out and you'd be good to go. If you're okay with this initial turbidity, go for it from day one!

Oh, and you shouldn't rinse this substrate. Use it right out of the bag.

One of the pleasant surprises of the "NatureBase" line has been that they do grow aquatic plants- quite well, actually. Surprising to us, because some of the ingredients that we used in our formulation aren't specifically well-known for growing plants. However, the others are more nutritious, and the "pluses outweigh the minuses", apparently! 

So, why do people want to use this stuff?

Well, If you understand the context for which they are intended, and the habitats which they help to replicate, the cloudiness and sedimentation is perfectly acceptable and logical...Of course, you need to make that "mental shift" to appreciate this stuff, right?

You can do all sorts of cool stuff with them. Hell, you can even mix them with commercial, off-the-shelf substrates to make cool, functionally aesthetic "custom" mixes of your own! We do this a lot, and come up with all sorts of interesting stuff!

Another interesting consideration is that these substrates have carefully-selected botanical materials in them, which, as we know, help foster microbial growth as they decompose, which creates the aquarium equivalent of an "active substrate!"

They're intended to help foster the growth of beneficial bacteria, biofilms, fungal growth, and micro crustaceans, to help build up a functional, diverse benthic habitat in botanical-style aquariums. They will help form the literal "base" of your botanical-style aquarium system (hence the name of the product line, "NatureBase").

 Is this starting to make more sense?

This falls perfectly in line with our intention to create a line of substrates that are more "microbiome-centric", helping shape the overall aquarium environment- not just a place to grow plants. 

We're doing some very exciting tweaking to the existing formulas, which will be debuting in a few weeks- as well as releasing some new and very exciting specialized versions of Nature Base...and a series of other substrate materials as well!

So, yes, in summary, the most important role of these substrates is to form a habitat for various microorganisms, crustaceans, and other creatures to colonize and multiply. And that requires a substrate which not only includes the aforementioned subsides, but the botanical components as well.

The mixing of materials not only looks interesting- it's a reflection of the diversity and vibrancy of the underwater environment. And it's exactly what you'll see in the wild habitat, too.

One of the things you notice in the images we share 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. We see organic detritus as an essential part of the substrate, and this influenced our philosophy when formulating NatureBase.

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.

 And of course, the whole idea of a rich, sediment-sand-and-soil substrate enriched with botanical materials is completely in line with the "best practices" we've developed as a community to create dynamic, botanical-style aquariums. In our case, not only will there be an abundance of trace elements and essential plant nutrients be present in such a substrate, there will be the addition of tannins and humic substances which provide many known benefits for fishes as well.

The best of both worlds, I think!

I hope this quick look at the NatureBase sedimented substrates answers a few lingering questions you might have had about them. And it probably has brought up a few more. No worries- we'll be revisiting this stuff more and more over the coming months!

Stay inspired, Stay creative. Stay fearless. Stay observant...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

March 15, 2021


From the depths of our imagination to the shallows of streams...

You're likely aware of the fact that we're crazy about small, shallow bodies of water, right? I mean, almost every fish geek is like "genetically programmed" to find virtually any random body of water irresistible!

Especially little rivulets, pools, creeks, and forest streams. The kinds which have an accumulation of leaves and botanical materials on the bottom. Darker water, submerged branches- all of that stuff...

You know, the kind where you'll find fishes!

Happily, such habitats exist all over the world, leaving us no shortage of inspiring places to attempt to replicate. Like, everywhere you look!

In Africa for example, many of these little streams and pools are home to some of my fave fishes, killifish! Of particular interest are the fishes of the genus Epiplatys. These fishes are outstanding at hiding and are quite adept at it in these little bodies of water, with their tangles of roots and submerged vegetation.

As mentioned above, many of these little jungle streams are really shallow, cutting gently through accumulations of leaves and forest debris.  Many are seasonal. The great killie documenter/collector, Col. Jorgen Scheel, precisely described the water conditions found in their habitat  as "...rather hot, shallow, usually stagnant & probably soft & acid."

Ah-ah! We know this territory pretty well, right?

I think we do...and understanding this type of habitat has lots of implications for creating very cool biotope-inspired aquariums. 

And why not make 'em for killifish?

So, for the most part, these fishes are often found in very shallow jungle streams. How shallow? Well, reports I've seen have stated that they're as shallow as 2 inches (5.08cm). That's really shallow. Like, seriously shallow! And, quite frankly, I'd call that more of a "rivulet" than a stream!

"Virtually still, with a barely perceptible current..." was one description. That kind of makes my case. Like, what you'd see when a small stream overflows it's banks and creates a smaller body of water. 

What does that mean for those of us who keep small aquariums?

Well, it gives us some inspiration, huh? Ideas for aquariums that attempt to replicate and study these compelling shallow environments...

An important consideration when contemplating such a replication in our tanks is to consider just how these little forests streams form. Typically, they are either a small tributary of a larger stream, with the path carved out by rain or erosion over time. In other situations, they may simply be the result of an overflowing tributary during the rainy season, and as the waters recede later in the year, they evolve into smaller streams meandering through vegetation.

Those little streams fascinate me.

These interesting little tributaries are usually shaded by trees at the margins, and often cut for many kilometers through dense rain forest. The bottoms of these tributaries- typically former forest floors- are often covered with seed pods, twigs, leaves, and other botanical materials from the vegetation above and surrounding them. Often, the water will pool into even smaller bodies of water.

In this world of decomposing leaves, submerged logs, twigs, and seed pods, there is a surprising diversity of life forms which call this milieu home. And each one of these organisms has managed to eke out an existence and thrive.

So-called "ephemeral" streams, typically occur only immediately after rain events (which means they usually don't have fish in them unless they are washed into them from more permanent watercourses). 

Now, I don't expect you to set up a tank with a water level that's 2 inches deep..And, although it would be pretty cool to do that, for more of us, perhaps a 3.5"-4" (8.89-10.16cm) of depth is something that can work? Yeah. Totally doable. There are some pretty small commercial aquariums that aren't much deeper than 8" (20.32cm), and you could adapt other containers for this purpose, right? 

We could do this with some of the very interesting South American or Asian habitats, too...Shallow tanks, deep leaf litter, and even some botanicals for good measure. 

Replicating these unique habitats creates functionally amazing aquariums, too!  These little bodies of water are very productive...


One of the more fascinating scientific observations I stumbled upon in recent years concerns the productivity (in terms of food inputs) of smaller Amazonian streams. It's long been known by science that the primary production of food in these streams has been our friend, allochthonous input- you know, leaves, wood, fruits, blossoms, etc. from the surrounding forests.

And, although there is a lot of "stuff" in these streams, biologists traditionally classified these habitats as "low in biomass." However, recent studies of the microfaunal diversity of these streams (Walker and Feriera), it was found that the stream fauna was aggregated in submerged litter and "may reach considerable densities..."

This observation suggested that the animal community within the submerged leaf litter banks was found in greater abundances- and was of greater importance- to the productivity of these waters than previously believed.


In other words, a lot of life and food happens in submerged leaf litter beds! They provide both food and shelter- two primary factors affecting population density among fishes. 

If we carry this out to its logical aquarium interpretation, it becomes more intriguing to contemplate an aquarium with the "hardscape" (for want of a better word) consisting essentially of leaves! 

Yeah, you've seen this before here. 

How about a long, low aquarium, like the ADA "60F", which has dimensions of 24"x12"x7" (60x30x18cm)? You would only fill this tank to a depth of around 5 inches ( 12.7cm) at the most. You'd use a lot of leaves to cover the bottom. We've done that a few times with great success.


in streams, the primary producers of the food webs that attract our fishes are algae and diatoms, which are typically found on rocks and wood wherever light and nutrients create optimum conditions for their growth. Organic material that enters streams via leaf fall is acted upon by fungi and small organisms, which help break it down.

It is probably no surprise, then, that bacteria (especially in biofilms!) and fungi are the initial consumers of the organic materials that accumulate on the bottom. Like, the stuff many of us loathe. These, in turn, are extremely vital to fishes as a food source.

Hence, one of the things I love so much about utilizing a leaf litter bed as a big part of your substrate composition in an aquarium! Of course, we talk about that all the time, right?

We do. And we'll continue to look into more ways to replicate these little shallow bodies of water in our aquariums, because the streams of the world are just a starting point for us to explore in our quest to create more realistic, functionally aesthetic aquariums that will provide enjoyment, education, and inspiration for others.

Stay inspired. Stay excited. Stay creative. Stay observant. Stay resourceful...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

March 12, 2021


The surprising benefits being flexible.

On of the annoying realities of our hobby- like life in general, is that sometimes you need to compromise stuff.

It's one of those words that us hobbyists naturally cringe when they hear, right?

You do. Admit it!

Compromise has such a feeling of "finality" about it, but the reality is that, in our hobby, compromising can often yield exciting results, unexpected benefits, and occasionally, breakthroughs. Sometimes, it's as simple as not being able to accommodate that one larger tank, and ending up with two, or even three smaller ones (in reality, is that EVEN a compromise for a fish geek?).

Or not being able to afford or obtain the one prized specimen of Apisto or whatever, and ending up with another species that you not only fall in love with, but learn to spawn, rear, and even foster breakthroughs with. Or thinking you were going be trying one type of aquascape, only to be "forced" into compromising a bit due to budget, space or time restrictions...only to end up with something amazing you never thought about before.


It happens. A lot. 

And it's not that bad a thing, really.

The reality is that being flexible, adventurous, and being willing to accept new ideas and approaches on perhaps a smaller scale or under a different set of circumstances is really one of the best traits that you can have as a hobbyist.

Compromising some aspects of an idea has, on so many occasions in my fishy "career", enabled me to accomplish stuff I never thought possible, with benefits, enjoyment, and opportunities that I could never have imagined previously. Especially when it comes to tank size- probably the most annoying compromise we as hobbyists feel that we have to make...Sometimes, the benefits of using a smaller tank might be surprising!

It's all really a matter of perspective. Think about it. What "compromises" have you made, only to come to realize that they were not compromises at all? 

When it comes to botanical-style aquariums, compromises require us as aquarist to make a bunch. When we understand that adding botanical materials to the aquarium, we're not only creating the environment- we're adding bioload to the system, and that we need to allow for the passage of time for the beneficial bacteria and other members of the microbiome to group and multiply within the system.

To many hobbyists, waiting for this microbiome to develop is a sort of compromise... We love stuff to happen fast! On OUR personal timeline. The reality, as we know by now, is that Nature sets the timeline, creates change, and requires us to accommodate HER- whether we want to or not!

Oh, sure, some of the changes that occur during the "life" of an aquarium are human-imposed, such as equipment modifications/replacements, aquascaping "edits", fish and plant additions, etc.

However, if you look carefully (as I'm sure that you do), as many changes can be attributed to the cycle of life which occurs in your little microcosm as to human "intervention" of the aquarium environment. 

You, the aquarist, ever keen on anything that occurs in your tank, will notice- and often perform subtle (or not-so-subtle) interventions to counteract this process, lest it descend into some sort of chaos, right? 

Yet, isn't "chaos" sort of a human-ascribed thing?

I mean, we're talking about changes in the aquatic habitat which evolve the look and perhaps the biological "operating system" of the aquarium. This is absolutely analogous to what happens in natural aquatic systems.

With a lot of botanical materials (terrestrial plants, branches, logs, leaves, etc.) in the water, one would anticipate some sort of chemical changes the longer the areas are submerged, and as these materials begin to decompose. And with a more-or-less constant influx of rain during the wet season, I would bet that there is some dilution or at least, redistribution, of organics within the ecosystem.  In our aquariums, redistribution is limited by hardscape (wood and rocks) much as it is in nature. And, one could make the argument that our water changes do, indeed simulate to some extent the processes of rainfall and flooding to some extent!

And our continuous addition, removal, and replacement of botanicals is, as many of us surmised, a pretty good replication of what happens in these systems in nature, as well. Materials are continuously falling into the water and being redistributed, with ones that have been down longer decomposing and/or being acted upon by fishes and other aquatic life forms.

Finding a "rhythm" that works for both us and our fishes is the key here. I mean, sure, if you want to really follow global weather patterns and do stepped-up water exchanges and botanical additions and removals to correspond with them, this would be a very cool experiment!

However, for most of us, simply establishing a routine of botanical additions and replenishment is a good idea.


And consistency. Working together in a most interesting way.

We've talked about it before, but it does bear some further review in this light: There are streams  where botanical accumulation (particularly in banks of leaf litter) has been going on more or less the same way for many years, creating semi-permanent features in the aquatic environment. For example, "meanders" (bends) in various Amazonian streams have been studied for some time, and some leaf litter beds are known to have existed for decades in the same place.

The implication for this is that such leaf litter beds become more-or-less-permanent habitats for generations of fishes and their offspring, and like the tropical reefs in the ocean- are an oasis of life- containing both the fishes and their prey items.

Now, although these are semi-permanent features in the habitat, they can vary throughout they year, influenced, as we discussed previously, by seasonal inundation. And then there are those floating leaf litter banks! It's been postulated by researchers that the floating litter banks supply the benthic community (which includes, of course, the fishes) with food and shelter, especially during the dry season when other habitats are unavailable.  

On the Amazonian floodplains, for example, the flood cycle of the rivers into the igapo are the dominant seasonal factor, and fish communities are found to fluctuate greatly over the year. During inundation, fish migrate into floodplain forests to feed on insects, fruits and seeds, among other things.


Studies of blackwater communities showed that, during these cycles, a greater diversity of fishes exists there. Many species were found to be specialized feeders. Fish, detritus and insects were the most important food resources supporting the fish community in both high and low water seasons, but the proportions of fruits, invertebrates and fish in their diets were reduced during the low water season.

Change, consistency, and compromise- yet again.

Obviously, there are numerous examples of this "yin/yang" sort of thing in Nature, all of which have profound and interesting implications and possibilities for hobbyists eager to attempt to replicate the "functional aesthetics" of such systems. The more we look at Nature, the more we find that trying to model our aquariums aesthetically and functionally after her processes is an amazing way to go.


And that involves compromises, doesn't it?

Perhaps the key to many previously overlooked benefits for our fishes is to simply try to emulate the processes which occur seasonally in nature..embracing change, and it's strange, yet inexorable relationship with consistency.

Our fishes have adapted to it. We should embrace it.

Some hobbyists have commented that, as their leaves and botanicals break down in their aquariums, and the 'scape as initially presented changes significantly over time. They know it or not, they are grasping the Japanese philosophy of "Wabi-Sabi"...sort of. One must appreciate the beauty at various phases to really grasp the concept and appreciate it. To find little vignettes- little moments- of fleeting beauty that need not be permanent to enjoy.


And, understanding these natural processes and replicating more and more of them in our aquariums can expose more and more people- even non hobbyists- to the wonder and fragility of these fascinating aquatic ecosystems, fostering a greater demand to protect them.

It's an amazing time to be an aquarist, isn't it?

I mean, we have the fishes, the technology, the materials, and the means to research arcane topics once considered solely the domain of scholars. We can actually execute on many of these things. We can try playing with concepts that we've likely never given much thought to previously. And we can rapidly communicate and share our ideas, successes, challenges, failures, and overall progress with fellow hobbyists all over the planet.

Nature is calling. 

Another thing for us to grasp...flexibility. Maybe it's even a mental shift?

Embrace the change that being flexible brings. Enjoy Nature at work. Assist, enjoy, and work with Nature in your aquarium, and you'll develop an even greater appreciation for the beauty of the natural world, and have a lot more fun doing so!

Stay engaged. Stay attuned. Stay observant. Stay creative. Stay flexible...

And Stay Wet.

Scott Fellman

Tannin Aquatics


March 11, 2021


Piling up

As you know, we're pretty into substrates around here!

And not just sand and gravel, as we've discussed repeatedly. Now, here's the thing: I am 100% certain that you can use all sorts of materials to create a functional and useful substrate for your aquarium. I've done this for many years with great success, as many of you have.

Long term management of our botanical-style aquariums has evolved along with the mindsets which accompany them. And this extends to how we treat our existing aquarium when we "remodel" it. 

Especially the substrate.


I think we need to stop "ditching" our "old"substrates when we iterate our tanks.

I know, the idea of leaving the substrate and leaf litter/botanical "bed" intact as you "remodel" isn't exactly a crazy one. And conceptually, it's sort of replicates what occurs in Nature, doesn't it?

Yeah, think about this for just a second.

As we almost constantly discuss, habitats like flooded forests, meadows, vernal pools, igarape, and swollen streams tend to encompass terrestrial habitats, or go through phases where they are terrestrial habitats for a good part of the year.

In these wild habitats, the leaves, branches, soils, and other botanical materials remain in place, or are added to by dynamic, seasonal processes. For the most part, the soil, branches, and a fair amount of the more "durable" seed pods and such remain present during both phases.

Beyond simply replicating these inundation/dry season cycles (ie; the "Urban Igapo" thing again), think about how materials, including detritus, accumulate in the substrate, and what the impact of removing this stuff is.

When you remove much of the hardscape, plants, etc. from the aquarium as you "evolve" it to something else, yet leave the substrate, some of the hardscape, leaves, etc. intact, you're essentially mimicking this process in a most realistic way.

Sure, a "makeover" of an aquarium can be a seriously disruptive event. On the other hand, if you take the mindset that this is a "transformation" of sorts, and act accordingly, it becomes more of an evolutionary process.

Leaving in the existing botanical substrate, along with its decomposing leaves, bark, sedimented material, detritus, and the accompanying biotia just makes a lot of sense, IMHO.

I mean, if you're not sold on the benefits that the biological continuity of leaving your "old" substrate intact bring, you can likely embrace the idea that decomposing leaves and such comprise a sort of aquatic "mulch" for plant growth, right? Mulch, by definition is: "Material (such as decaying leaves, bark, or compost) spread around or over a plant to enrich or insulate the soil."

What works in the garden likely works in the aquarium, in the context of "substrate enrichment", right?

I think that the possibility of utilizing botanicals along with specialized substrates as a means to grow plants and enrich the overall aquarium ecosystem on many levels is simply too irresistible to overlook. We've talked about this before. Indeed, botanicals are a sort of "substrate" in and of themselves- and that is something that's quite interesting! 

Yes, we've talked about this almost constantly for years.

And they are ALIVE.

The idea of considering the substrate of your aquarium a living, breathing organism makes you take a different mindset. I mean, would you essentially kill an entire ecological niche within your tank simply because you want a "do-over" on the hardscape, plants, or other part of the "theme?" 

Not if you look at it like that, right?

Just because you were doing a South American-inspired tank, and now you're going African- if the water parameters are intended to basically be the same, what's the point in decimating an entire functioning substrate in the process?

That's not "progress"- that's a huge setback!

The typical justification for ditching the old substrate during a tank "remodel" is that you want to "get rid of all of the detritus that's accumulate in the substrate..."

Wait a minute!

If we really look at it objectively, "detritus" plays a very important role on our systems. It not only provides a physical place for positive biological activity which supports the overall function of the aquarium- it fuels it.


With our embrace of "detritus" or "mulm" as a source of "fuel" for creating active biological systems within the confines of our aquariums, I think that the idea of an "enriched substrate" will become an integral part of the overall ecosystems that we create. Considering the substrate as both an aesthetic AND functional component- even in "non-planted" aquariums, opens up a whole new area of aquarium "exploration."

I envision that the future of mainstream aquarium practice may include creating such a substrate as simply part of "what we do." Adding a mix of botanical materials, live bacterial and small organism cultures, and even some "detritus" from healthy aquatic systems may become how we establish systems. And leaving the existing materials alone and building upon them will be the way.

These ideas are cool.

Cool, because they force us to look at Nature in a different way. Cool- because they make us consider not only the "appearance", but the (wait for it...) function of  the natural habitats we're fascinated by and the aquariums which we develop to replicate them.

So, it's okay to let things "pile up" now and then, right? 

I think so.

Today's simple, but important thought.

Stay curious. Stay brave. Stay motivated. Stay excited...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



March 10, 2021


Our friends, the fungi


We're likely the only fish geeks you'll encounter who constantly sing the praises of biofilms and fungi huh? 


Yeah, those guys.

They're all over our botanical-style aquariums, regardless of how we feel about them....

Not the ones that we vilify for attacking our fish or their eggs, of course. It's easy to just heap them in with the "bad guys" and the nasty implications they have. 

Nope. There's more to it than that.

Fungi are "omnipresent" in aquatic ecosystems- even our allegedly "pristine" aquariums. 

Fungi reproduce by releasing tiny spores that then germinate on new and hospitable surfaces (ie, pretty much anywhere they damn well please!). These aquatic fungi are involved in the decay of wood and leafy material. And of course, when you submerge terrestrial materials in water, growths of fungi tend to arise.

Anyone who's ever "cured" a piece of aquatic wood for your aquarium can attest to this!

Fungi tend to colonize wood because it offers 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?

And of course, fishes and invertebrates which live amongst and feed directly upon the fungi and decomposing leaves and botanicals 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! 

Interestingly, many fungi are "specialists", with what ecologists classify as "Ingoldian anamorphic fungi" being most numerous on decaying leaves, while fungi known as ascomycetes (order Dothideomycetes, Sordariomycetes) are prevalent on submerged/exposed woody substrata, like twigs, tree trunks, and bark. Unique fungi are found in tropical waters and differ from those in temperate locations.

There are around 3000 species that are known to be associated with aquatic habitats! That's A LOT of species!

Aquatic “true fungi” are known as "osmoorganotrophs", a fancy way of saying that they absorb nutrients across their cell wall. Most of them have a "filamentous" morphology at some point during their life cycle. This morphology enables them to invade deep into substrates and to directly digest particulate organic matter (POM) to acquire nutrients for growth and reproduction. 

The fungal community consumes microscopic algae, aquatic macrophytes and terrestrial plant litter (including wood). Aquatic fungi act as very significant decomposers of particulate organic matter (POM), specifically coarse particulate organic matter (CPOM), which includes both plant and animal material . 

We see this in Nature- and absolutely in our aquariums!

The aquatic fungi which will typically decompose leaf litter and wood are the group known as “aquatic hyphomycetes”. Another group of specialists, "aero-aquatic hyphomycetes," colonize submerged plant detritus in stagnant and slow- flowing waters, like shallow ponds, puddles, and flooded forest areas. Fungal communities differ between various environments, such as streams, shallow lakes and wetlands, deep lakes, and other habitats such as salt lakes and estuaries.

And we see them in our own tanks all the time, don't we?

As we know by now, fungi play a huge role in the decomposition of leaves, both in the wild snd in the aquarium. By utilizing special enzymes, aquatic fungi can degrade most of the molecular components in leaves, such as cellulose,, hemicelluloses, starch, pectin and even lignin.

Depending on various factors, such as leaf litter type and the local water chemistry, fungal decomposition of leaves can take anywhere from 1 month to 6 months.

The fungi known as aquatic hyphomycetes produce enzymes which cause leaf maceration, and in as little as 2 to 3 weeks, as much as 15% of the decomposing leaf biomass in many aquatic habitats is processed by fungi, according to one study I found.

Fungi, although not the most attractive-looking organisms, are incredibly useful...and they "play well" with a surprisingly large number of aquatic life forms to create substantial food webs, both in the wild and in our aquariums!

Natural habitats are absolutely filled with this's like the whole game here- an explosion of life-giving materials, free for the taking...

Another "mental shift", I which many of you have already made, no doubt. I certainly look forward to seeing many examples of us utilizing "what we've got" to the advantage of our fishes! AGAIN: 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- but as supplemental food sources to "power" the life in our tanks.

And of course, as we've discussed many times here, fungi are actually an important food item for other life forms in the aquatic environments tha we love so much!  In one study I stumbled across, gut content of over 100 different aquatic insects collected from submerged wood and leaves showed that fungi comprised part of the diet of more than 60% of them, and, in turn, aquatic fungi were found in gut content analysis of many species of fishes!

Still need more convincing about the value of fungi to food webs? Check out this passage from a paper I found by Werzbacher Christian, et al.:

"Microbial mineralisation of plant litter supports a complex food-web including all kinds of microbes (Archaea, Bacteria, fungi, protozoans) and invertebrates (nematodes, trematodes, gammarids, insects, snails). As a consequence, plant litter even supplies top predators such as crayfishs, amphibians, birds, fishes and bats with organic matter and energy via the microbial food web. The main basis of the microbial food web consists of fungi and bacteria growing in and on the plant debris..."

Fungi perform key roles in transferring terrestrial materials, like leaves- otherwise unavailable for aquatic organisms - to higher trophic levels. Ya' know- like, our fishes!

These small, seemingly "annoying" life forms are actually the most beautiful, elegant, beneficial friends that we can have in the aquarium. When they arrive on the scene in our tanks, we should celebrate their appearance.

Stay the course.

Don't be afraid.

Don't reach for the scrub brush.

Open your mind.

Study what is happening. Draw parallels to the natural aquatic ecosystems of the world. Look at this with wonder, awe, and courage. And know that the pile of decomposing goo and fungal strands that you're looking at now all over your leaf litter is just a metaphorical "stepping stone" on the journey to an aquarium which embraces Nature in every conceivable way.

Stay inspired. Sty curious. Stay patient. Stay open-minded...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


March 09, 2021


"Operating our aquariums...Replicating Nature"

One of the real “frontiers” of the aquarium hobby is the practice of “operating” our tanks like the little microcosms that they are.

Attempting to replicate in our aquariums- on a number of levels- the processes and cycles which occur in Nature. We’re talking about things like seasonal weather cycles, water temperature, depth, nutrient levels, pH, current, photoperiod, food “pulsing”, etc.

Historically, hobbyists have been doing things like this to stimulate spawning in a wide variety of fishes over the years. This is really nothing new.

However, incorporating regular environmental manipulation for the routine maintenance of our fishes IS something a bit different. I'm not talking about "working" your tap water to achieve "blackwater" or "brackish" conditions in your aquarium. Rather, I'm suggesting that, once those "baseline" environmental parameters are set, that you "operate" your tank by trying to replicate some of the processes that we mentioned above.

And we're just scratching the surface here!


One easy "operation" that we can perform is the seasonal "pulsing" of leaves into our tanks. It's a process which can relatively easily simulate what occurs in Nature, when you think about it. 

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!

And, for the fishes and other organisms which live in, around, and above the litter beds, there is a lot of potential food, which does vary somewhat between the "wet" and "dry" seasons and their accompanying water levels. The fishes tend to utilize the abundant mud, detritus, and epiphytic materials which accumulate in the leaf litter as food. During the dry seasons, when water levels are lower, this organic layer compensates for the shortage in other food resources. 

During the higher water periods, there is a much greater amount of allochthonous input (remember that? I mean, on what other hobby-related site do they talk about THAT shit, huh?) from the surrounding terrestrial environment in the form of insects, fruits, and other plant material. I suppose that, in our aquariums, it's pretty much always the "wet season"in that regard, right?

We tend to top off and replace decomposing leaves and botanical more-or-less continuously, allowing materials to decompose and accumulate on top of one another. Very similar to what happens in Nature.

And it makes me wonder...

What if we stopped replacing leaves and even lowered water levels or decreased water exchanges in our tanks to correspond to, for example, the Amazonian dry season (June to December)...And if you consider that many fishes tend to spawn in the "dry" season, concentrating in the shallow waters, could this have implications for spawning our fishes?

I think it might.

In fact, I further proffer that we need to look a lot deeper into the idea of environmental manipulation for the purpose of getting our fishes to be healthier, more colorful. Now I know, the idea is nothing new on a "macro" level- we've been increasing and lowering temps in our aquariums, adjusting lighting levels, and tweaking stuff for a long time in attempts to breed them. That's kind of "Exhibit #1" in making the case that these types of processes work.


Killie keepers have played with this in drying and incubation periods in annual killifish eggs. However, I don't think we've been doing a lot of real hardcore adjusting water levels, increasing nutrient levels (ie; "pulsing" adding leaves and other botanicals), manipulating current, dissolved oxygen, food types, etc. 

I think that there are so many different things that we can play with- and so many nuances that we can investigate and manipulate in our aquariums. What about the pulsing of leaf additions to correspond to the seasonal leaf drop?

I think that this could even add a new nuance to biotope aquarium simulation and the contest scene, such as creating an aquarium which simulates the actual functions- not just the "look"- of  the "Preto da Eva River in Brazil in October", for example...with appropriate environmental conditions, such as water level, amounts of allochthonous material, etc. Show those hardcore contest biotope snobs what a real biotope aquarium is all about! 😆

The possibilities are endless here! And, as always, the aesthetics are a "collateral benefit" of the process.

So much to consider.

Of course, we're doing this stuff for a reason: To create more naturally-functioning, authentic-looking, aquatic displays for our fishes. To understand and acknowledge that our fishes and their very existence is influenced by the habitats in which they have evolved. To unravel the subtleties of the relationship between them on a deeper level.

Wild tropical aquatic habitats are influenced greatly by the surrounding geography and flora of their region, which in turn, have considerable influence upon the population of fishes which inhabit them, and their life cycle. The simple fact of the matter is, when we add botanical materials to an aquarium and accept what occurs as a result-regardless of wether our intent is just to create a different aesthetic, or perhaps something more, we are-to a very real extent-replicating the processes and influences that occur in wild aquatic habitats in Nature.

The presence of botanical materials such as leaves in these aquatic habitats is fundamental. They're part of Nature's "operating system." 


In our little hobby sector, leaves are sort of the "gateway drug", if you will, into our world. Where you go from there depends upon what aspects of the "operating system" you're determined to play with!

The manipulation of other aspects of the aquarium environment, such as temperature, water current, and lighting is every bit as important as the the physical additions of botanical materials and leaves, when it comes to the impact that they have. Even factors such as "filling" a tank with more and more roots and other materials after it's "underway" is another simulation of Nature that we could play with. 

Of course, even when "operating" our tanks, we need to deploy radical amounts of patience in our work.

Botanical-style aquariums typically require more time to evolve. This process can be "expedited" or manipulated a bit, bit to achieve truly meaningful and beneficial results, you just can't rush stuff! 

You can't interrupt it, either.

When you do, as we've learned, results can be, well- "different" than they would be if you allow things to continue on at their own pace. Not necessarily "bad"- just not as good as what's possible if you relax and let Nature run Her course without interruption.

Patience is our guideline. Nature our inspiration. Experience and execution our teachers. We're on a share the benefits which can be gained by embracing and meeting Nature as She really is.

Give Her a chance. let's let Nature do her thing without interruption.

Trust me. She's awfully good at it.

In the confines of an aquarium, finding a "rhythm" that works for both us and our fishes is the key here. I mean, sure, if you want to really follow global weather patterns and do stepped-up water exchanges and botanical additions and removals to correspond with them, this would be a very cool experiment!

However, for most of us, simply establishing a routine of botanical additions and replenishment is a good idea. Removing them as they decompose, or leaving them in until they completely break down are both practices which form part of the "management"- the operating system- of our aquariums. 


And consistency. 

Working together in a most interesting way.

The more we look at Nature, the more we find that trying to model our aquariums aesthetically and functionally after Her processes is an amazing way to go!

And I think that our fishes will let us know, too...I mean, those "accidental" spawnings aren't really "accidental", right? They're an example of our fishes letting us know that what we've been providing them has been exactly what they needed.

It's worth considering, huh?

Stay creative. Stay observant. Stay diligent. Stay persistent. Stay patient...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

March 08, 2021


The Urban Igapo in practice...

It's been about 4 years since we first presented our idea for replicating the flooded forests and meadows of South America (Igapo and Varzea).

In a fun homage to the hobby, we called the concept the "Urban Igapo." About 2 years ago, we went more in depth with some of the procedures and techniques that you'd want to incorporate into your executions of the idea.

Here are some answers to a few of the most common questions we receive on the idea.

Do I have to have a "dry season?"

Well, that's a good question! I mean, the whole idea of this particular approach is to replicate as faithfully as possible the seasonal wet/dry cycles which occur in these habitats. It starts with a dry or terrestrial environment, managed as such for an extended period of time, which is gradually flooded to simulate inundation which occurs when the rainy season commences and swollen rivers and streams overflow into the forest or grassland.

Sure, you can replicate the "wet season" only- absolutely. I've seen tons of tanks created by hobbyists to do this. However, if you want to replicate the seasonal cycle- the real magic of this approach- it's more fun to do the "dry season!"

Think of it in the context of what the aquatic environment is- a forest floor or grassland which has been flooded. If you develop the "hardscape" (gulp) for your tank with that it mind, it starts making more sense. What do you find on a forest floor or grassland habitat? Soil, leaf litter, twigs, seed pods, branches, grasses, and plants.

 Just add water, right?

What size aquarium do you need? 

You can use just about any size of aquarium. Most of my executions have been in smaller tanks (1-10 U.S. gallons). Of course, you can scale this up to medium and large aquariums. The concept is the same.The execution is the same. The biggest challenge, in my opinion, is embracing the fact that you might set up a large tank which may not have any fishes in it for months. Patience! It's a mental shift; a commitment to following though on an idea that is rather "alien" to most aquarists.

Does the grass and plants that you've grown in the "dry season" survive the inundation?

Another great question. Some do, some don't. (How's that for concise info!). I've played with grasses which are immersion tolerant, such as Paspalum. This stuff will "hang around" for a while while submerged for about a month and a half to two months, in my experience, before ultimately succumbing. Sometimes it comes back when the "dry season" returns. However, when it doesn't survive, it decomposes in the now aquatic substrate, and adds to the biological diversity by cultivating fungi and bacteria.

You can use many plants which are riparian in nature or capable of growing emmersed, such as my fave, Acorus, as well as all sorts of plants, from Hydrocotyle, Cryptocoryne, and others. These can, of course, survive the transition between aquatic and "terrestrial" environments.

How long does the "dry season" have to last?

Well, if you want to mimic one of these habitats in the most realistic manner possible, follow the exact wet and dry seasons as you'd encounter in the locale you're inspired by. Alternatively, I'd at least go 2 months "dry" to encourage a nice growth of grasses and plants prior to inundation.

And of course, you cans do this over and over again! 

When you flood the tank, doesn't  it make a cloudy mess? Does the water quality decline rapidly? 

Sure, when you add water to what is essentially a terrestrial "planter box", you're going to get cloudiness, from the sediments and other materials present in the substrate. You will have clumps of grasses or other botanical materials likely floating around for a while.

Surprisingly, in my experience, the water quality stays remarkably good for aquatic life. Now, I'm not saying that it's all pristine and crystal clear; however, if you let things settle out a bit before adding fishes, the water clears up and a surprising amount of life (various microorganisms like Paramecium, bacteria, etc.) emerges. Curiously, I personally have NOT recorded ammonia or nitrite spikes following the inundation. That being said, you can and should test your water before adding fishes. You can also dose bacterial inoculants, like our own "Culture" or others, into the water to help.

Should I use a filter in the "wet season?"

You certainly can. I've gone both ways, using a small internal filter or sponge filter  in some instances. I've also played with simply using an air stone. Most of the time, I don't use any filtration. I just conduct partial water exchanges like I would with any other tank- although I take care not to disturb the substrate too much if I can. When I scale up my "Urban Igapo" experiments to larger tanks (greater than 10 gallons), I will incorporate a filter. 

What kinds of fishes can you keep in these systems?

I've played with a lot of different types of fishes. Particularly annual killifishes, small characins (like Red Phantom Tetras, Neons, and others), Gouramis, and Bettas. Lots of possibilities!

Okay, let's wrap this for today...A lot of orders to ship!

We will re-visit this topic again in the near future; it's becoming a very popular idea, and there are a lot more questions!

And we're excited to see it develop more!

Stay excited. Stay innovative. Stay curious. Stay observant. Stay patient...

And Stay Wet.


Scott Fellman 

Tanni nAquatics