The "bottom-up evolution" is here...

I know, I know- I seem like I bring up variations of the same subject like 100 times in this blog. However, I think there's good reason to do so. I mean, many of the ideas that we have postulated and played with have not only "worked"- they've led to other tangential discoveries, practices, evolutions, and occasionally, breakthroughs! 

SO...For the "umpteenth" time, let's talk a bit more about...wait for it- substrates. 

Yeah. The bottom of your tank. Or, more precisely, the stuff that comprises it. 

I'm obsessed with this shit, as you know.

SECRET: Literally, if I didn't start Tannin, I'd have created a company that only curates and sells substrate materials...So,to scratch this itch that's never went away, I'm doing the next best thing in 2020- we'll be increasing the diversity of our substrate offerings. Stuff you won't find elsewhere, destined for applications that no one else could ever love more than our community. Stay tuned...

Anyways- back to the topic at hand...

Now, for many of us, the literal "foundation" of our aquariums has been- and still is- sand or gravels. It's been that way for most of the century of the modern aquarium keeping era. Sure, there have been variations in grades, sand types and origins, and colors and such, but it's basically the same stuff we've had forever.

Sands and gravels are  a good simulation of the materials found many natural habitats. However, I think we have to accept that many aquatic habitats aren't simply sand and gravel- our sort of idealized, sanitized vision of what the bottom should be.

When you consider natural waters and the impact of the substrate, the story gets even more interesting. In rivers, such as the Amazon, Rio Xingu, or Orinoco, you'll find materials that originate in the mountains and highlands, and gradually work their way downstream, influencing the aquatic environment chemically, physically, and geographically. 

The materials are influenced by the currents and water movement, tend to "sort themselves out", and re-organize over time. To simulate this dynamic, it pays to do a little research on the specific environment that you're looking to replicate. Some parts of the Amazon, for example, are replete with larger particles of material, even rock, with a covering of fine sand.

Studies have shown that particle sizes tend to decrease the further downstream from the source they are found. Makes sense, right?

Large rivers, such as the Amazon, have beds of shifting sands, slowly transported with the currents. Typically, the larger the item (pebble, rock, or boulder), the longer it tends to stay in one place. So, in a more powerful flow, you're more likely to find larger-sized materials.

History lesson (yeah- where else in the aquarium world will you get a mini history lesson on substrates?):

The first recorded observations of bed material of the Amazon River were made in 1843 by Lt. William Lewis Herndon of the US Navy, when he travelled the river from its headwaters to its mouth, sounding its depths, and noting the nature  of particles caught in a heavy grease smeared to the bottom of his sounding weight. He reported the bed material of the river to be mostly "sand and fine gravel." Oltman and Ames took samples at a few locations in 1963 and 1964, and reported the bed material at Óbidos, Brazil, to be "fine sands, with median diameters ranging from 0.15 to 0.25 mm."

Okay, not some real breakthrough knowledge there, I know- but the point is, many of the larger rivers and their tributaries that we obsess over have mixed sizes of sands and gravels on the bottom.

There is a LOT to the science of naturally "graded" materials, and you'll have to do some research on the subject. In the end, science can tell you a lot; however, creativity and your aesthetic taste are typically the "guidelines" that you'll embrace to assemble your "slice of the bottom."

With an abundance of commercially-available substrate materials on the market, it's easier than ever to replicate cool little segments of the environment. Take a sort of 'holistic" approach to constructing the substrate in your aquarium. Look into the practical and aesthetic aspects of your materials, and how you'd combine the permanent materials (gravels, sands, pebbles, etc.) with the more "transient" materials (i.e.; botanicals and leaves). It's a lot of fun, very engaging, and can almost create a "hobby within a hobby!"

And yeah, the "transient materials" part is equally fascinating to me.

In many of the slower-moving waters, where the sediment "sorting" has already occurred, you will find an accumulation of softer, more "ephemeral" materials, like leaves, twigs, seed pods, soil, sediments, etc. over a bed of sand. Sometimes, these can be quite deep- a meter or more. In areas such as the Pantanal, as related by our friend, Tai Strietman, this decomposing materials- often terrestrial plant parts and such, can be extremely deep.

What goes on in these deep beds of decomposing botanical materials?

A lot, I think.

It's something that I keep coming back to, because the idea of utilizing botanicals in your aquarium substrate keeps tantalizing me with its performance and potential benefits.

As I've obsessively reported to you, last year, I set up a small tank in my office for the sole purpose of doing damn near the entire substrate with leaves and twigs- sort of like in Nature. There was less than approximately 0.25"/0.635cm of sand in there. I went from throwing in wood to make it look "cool", to ultimately yanking out everything but the leaves and twigs on the bottom. That's the whole "scape." What we in the reef world call a "no scape." 

Leaves and a shoal of Parachierdon simulans. 

Nothing else.

And the interesting thing about this tank was that it was one of the most chemically stable, low-maintenance tanks I've ever worked with. It held a TDS of 12 and a pH of 6.2 pretty much from day one of it's operation. It cycled in about 5-6 days. Ammonia was barely detectible. Nitrite peaked at about 0.25mg/L in approximately 3 days. 

Now, the point of this piece is not to drop a big old "humble brag" about some new tank I started. The point is to show what I think is an interesting "thing" I noticed about that tank: Stability and ease of function.

I was quite astounded how a new tank could go from dry to "broken in" in a week or so. And not just "broken in" (ie; "cycled"), mind you. We're talking, like, stable. I don't usually do this, but I tested all basic parameters every day for the first 3 weeks of the tank's existence, just to kind of see what would happen.

And not much happened.

The interesting thing about a tank like this is that it relied on leaves in a way that I had rarely done before. Yet, I had complete confidence that it could work just fine. I'm not some "visionary" here- I'm just a guy who's played with blackwater/botanical-style aquariums for a long time and has developed a certain degree of comfort with them.

Many of you are in the same position, I'll bet!

As far as I have determined, what goes on in an aquarium with botanicals- or leaves, in this instance as the total  "substrate" or "hardscape", as the case may be, is that they become the basis for biological activity in the tank. As we have discussed a million times here, as botanicals break down, they recruit bacteria, fungi, and other organisms on their surfaces.

What I am starting to feel more and more confident about is postulating that some degree of denitrification occurs in a system with a layer of leaves and botanicals as a major component of the tank. At the very least, good nutrient processing occurs in such a system because of the resident micro and microfauna present in this botanical bed.

Now, I know, I have little rigorous scientific information to back up my theory, other than anecdotal observations and even some assumptions. However, there is always an example to look at- Nature. 

Of course, Nature and aquariums differ, one being a closed system and the other being "open." However, they both are beholden to the same laws, aren't they? And I believe that the function of the captive leaf litter bed and the wild litter beds are remarkably similar to a great extent.

The thing that fascinates me is that, in Nature, leaf litter beds perform a similar function; that is, fostering biodiversity, nutrient export, and yes- denitrification. Let's take a little look at a some information I gleaned from the study of a natural leaf litter bed for some insights.

In a slow-flowing wild Amazonian stream with a very deep leaf litter bed, observations were made which are of some interest to us. First off, oxygen saturation was 6.7 3 mg/L (about 85% of saturation), conductivity was 13.8 microsemions, and pH was 3.5.

Some of these parameters (specifically pH) are likely difficult to obtain and maintain in the aquarium, but the interesting thing is that these parameters were stable throughout a months-long investigation.

Oxygen saturation was surprisingly low, given the fact that there was some water movement and turbulence when the study was conducted. The researchers postulated that the reduction in oxygen saturation presumably reflects respiratory consumption by the organisms residing in the litter, as well as low photosynthetic generation (which makes sense, because there is no real algae or plant growth in the litter beds). And of course, such numbers are consistent with the presence of a lot of life in the litter beds.




Microscopic investigation confirmed this- it revealed that the leaf litter was heavily populated with fungi and other microfauna. There was a significant amount of fish life. Interestingly, the fish population was largely found in the top 12"/30cm of the litter bed, which was estimated to be about 18"/45cm deep. The food web in this type of habitat is comprised largely of fungal and bacterial growth which occurs in the decomposing leaf litter. 

Okay, I"m throwing a lot of information here, and doing what I hope is a slightly better-than-mediocre attempt at tying it all together. The principal assertions I'm making are that, in the wild, the leaf litter bed is a very productive place, and has a significant impact on its surroundings, and that it's increasingly obvious to me that many of the same functions occur in an aquarium utilizing leaf litter and botanicals.

I think that it's time that we as hobbyists devote a bit more time and effort to the idea of "alternative substrates"- or, at the very least, utilizing more than just sand and gravel for our substrates and calling it a day.

There is so much more that I think we can learn by incorporating botanical and other materials into our aquarium substrates. It's part of the reason why we've offered various "substrate additives" in the form of crushed leaves, bark, twigs, coconut-based materials, etc. for the past 4 years or so.

We're going to double down on this stuff...Sands, botanicals, clays, and other stuff...

I think that the bottom of our aquariums is so much more than just a place to secure our driftwood, rocks, and plants. It's an opportunity- a place to enhance, augment, or even drive the biological and chemical environment of our aquariums. 

If we continue to look to the natural aquatic habitats from where our fishes come, there is literally a whole new world of possibilities. Possibilities to create aesthetically unique, visually compelling, and entirely functional microhabitats within our botanical-stye aquariums. This is literally an untapped area of the hobby, which is screaming at us to do more and make some discoveries and breakthroughs.

Now, with much deference to the planted aquarium crowd, particularly those who play with "dirted" substrates- we can build on this. Of course, we're not taking about utilizing alternative substrates strictly for growing plants, like those cool cats are. Nope, we're talking about utilizing such materials in a more "holistic", fish-focused aquarium, centering on replicating the look and function of natural aquatic habitats. 

We're going to be talking a lot more about this in 2020. We're going to think about how to incorporate all sots of materials and ideas into our substrates.  And yes, the long-awaited, much discussed "Urban Igapo" soils will be coming very soon. It's time to experiment.

A literal "active substrate", indeed! Yet, something that is fascinating and beautiful for those who give the idea a shot!

This is a big aesthetic shift in the hobby, but it goes well beyond that.

We're literally going to elevate the substrate from being at the bottom (metaphorically) to being top-of-mind (or, at least higher up in our consideration process) when designing and executing our new botanical-style aquariums.

The result of this focus- we hope- will be a greater understanding of the form, function, and even the aesthetics that the substrate can bring to the aquarium. Mental shifts are just the beginning; you've already made that "commitment" the minute you set up your first tank of decomposing leaves and such.

Yeah, you're in!

And we recognize that we are all part of a greater whole, and that the work that we're doing will benefit the generations of aquarists who will follow us, and apply what we're learning in ways that we probably haven't even contemplated yet. Thinking about things like botanical-infused substrates are just one way to push the state of the art along.

Yeah, it's a hobby evolution...from the bottom up.

Glad to have you in the mix!

Stay excited. Stay inspired. Stay diligent. Stay open-minded. Stay hungry for knowledge...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


2 Responses

Scott Fellman
Scott Fellman

December 22, 2019

Ohh- good find! I think you’re on to something here- I have felt that they serve as a carbon source much like the vodka dosing, etc. you describe. It really deserves more research from those equipped to do it! So much to learn! Yeah, I think leaves are the literal “fuel” for our biological ’operating systems" in botanical-style aquariums!


Joshua E Morgan
Joshua E Morgan

December 22, 2019

While researching how to make leaf mould as a planting additive, I have read that leaves – upon entering the water – have 30 times a much organic carbon as nitrogen. Denitrifying bacteria need to have carbon present to ‘breathe’ nitrate…perhaps this is how denitrifying works so effectively in the presence of leaves? Certainly less potential for trouble than adding vinegar, methanol, or vodka as the carbon sources.

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