In the mix...literally.

There is something about the materials that we place on the bottom of our aquariums, collectively known as "substrates"- which has always appealed to me.

I find them compelling and fascinating in both form and function. 

And it's not like I see substrates as just a package of sand or gravel. It's about a combination of materials, used to create what I like to call "functionally aesthetic" effects. Yeah, I've always looked substrate materials the way other people look at cocktails:

It's about mixing stuff.

Yeah, seriously. 

Substrates in Nature are not always just uniformly comprised of one material. Rather, they're aggregations of various materials, ranging from geological materials (rocks, sand, etc.) to botanical materials, like leaves, roots, etc., and sediments (clays, etc.).

Now, in Nature, there are numerous factors which contribute to the composition of aquatic substrates , including geology, the flow velocities of the body of water, the surrounding topography, the seasonal variations in water level (ie; inundation/dessication cycles), and accumulation of materials from the surrounding terrestrial environment.

There's a whole scientific field of study about this stuff.

So, why the hell do we as hobbyists, who want to create" the most realistic approximations of wild habitats possible", always seem to just "mail it in" when it comes to substrate? I mean, for a lot of hobbyists, it's just "open a bag of _____________ sand or whatever, and call it a day" and move on to the more "exciting" parts of our tank?

I think we just rely on the commercially available stuff- and that's that.

Kind of sad. Kind of...short-sided, really.

Now, in defense of the manufacturers of sands and gravels for aquarium use- I love what they do, and what they have available. These items are of generally excellent quality, provide a wide range of choices for a variety of applications, and are readily available. Most are fantastic.

Yet, they're not the "end-all/do-all" solution, IMHO.

We can, and should go further.

Most commercially available aquarium substrates are a great "starting point" for creating more dynamic ecosystems for our aquariums. Kind of like tomato puree is to pasta sauce...a beginning! Sure, you can use just the puree and enjoy your "sauce", but isn't it always better to add a bit of this and that and build on the "base"to create something better?

It is.

And we can.


And another thing:

I have concluded- after a lifetime in the aquarium hobby, and decades of researching and visiting natural aquatic habitats of all types-that the substrate in most wild ecosystems is...well- kind of "dirty." 

"DIrty" isn't what you think, however.

It's not "dirty" in the "polluted" sense...

"Dirty" in the sense of it not being sterile or pristine the way we like to keep our substrates in aquariums.

Think about it:

Over the past century or so of the aquarium hobby, it's become pretty much "doctrine" that we don't allow stuff like uneaten food, fish waste, or "detritus" to accumulate in the substrate. We're implored to regularly siphon this stuff out of our substrate and discourage its accumulation at all costs.

Now, on the surface, I totally get this. Some of it is "Aquarium Hobby 101" kind of stuff.

Allowing uneaten food and excessive amounts of fish waste to accumulate in your sand bed is conceivably a recipe to create a "nutrient sink" which will begin degrading the water quality of your aquarium. So, we remove it...Sound advice, sure.

I mean, no one wants to have increasing phosphate, nitrate, and other organic compounds accumulating in their tank, right?

I've seen many recommendations in aquarium content over the years to siphon out your substrate weekly or monthly. Now, again, I don't have a problem in us preaching good habits to new aquarists: Don't overstock. Don't overfeed. Filter your aquarium properly. Complete regular water exchanges. I mean, sure, these are foundational "best practices", and part of the fundamentals of keeping fishes in a closed aquatic systems for the widest variety of hobbyists.

That being said, if you're NOT overfeeding, NOT overstocking, and conducting regular water exchanges in your aquarium, why is there a necessity to thoroughly siphon the substrate frequently?

Think about it for a second before you go and pelt me with stones for my heretical questioning of this "fundamental" practice in aquarium keeping. The reality is that we have been urged to siphon out "stuff" from the substrate for fear of it accumulating and degrading water quality, right?

Okay, sounds good. However, consider that, in an otherwise well-managed aquarium, the organics in the substrate bacteria and other organisms which live within it.  

Ask yourself why we try to seek a balance of life forms within our aquairum.

And, we embrace good husbandry because we want to facilitate the proper biological function within the system. And that means, "partnering" with our friends, the bacteria- to facilitate nutrient processing. Not trying to wipe them out on a continuous basis!

So, if you're a typical aquarist, and run a properly stocked aquarium, and embrace generally accepted husbandry practices, it seems to me that aggressively siphoning the substrate is essentially removing food resources from the bacteria and other organisms which live within the substrate.  The very organisms which we rely upon to keep our little ecosystems thriving!

So, it's actually counterproductive.

Yeah- in our effort to keep the tank "clean", we are actually starving these organisms, and creating a sort of "dependency" on our aggressive, artificially imposed maintenance practices.

Much of the organic detritus we fear is an essential "component" of the substrtae- in both Nature, and in a natural aquarium system...

Okay- back to Nature for now:

When we started Tannin, my fascination with the varied substrate materials of tropical ecosystems got me thinking about ways to more accurately replicate those found in flooded forests, streams, and diverse habitats like peat swamps, estuaries, creeks, even puddles- and other bodies of water, which tend to be influenced as much by the surrounding flora (mainly forests and jungles) as they are by geology.

It's turned into a minor obsession, and I've learned a lot along the way.

Many substrates in tropical regions which are subject to seasonal flooding are comprised of a unique class of soil, the"Podzols" -soils characterized by a whitish-grey subsurface, bleached by organic acids. They have an overlying dark accumulation of brown or black illuviated humus. These soils support the rainforests surrounding blackwater streams, yet are the most infertile soils in Amazonia. 


And of course, my obsession with botanical materials to influence and enrich the aquarium habitat caused me to look at the use of certain materials for what I call "substrate enrichment" - adding materials reminiscent of those found in the wild to augment the more "traditional" sands and other substrates used in aquariums. 

And in some instances, to replace them entirely.  

Now, in many of the tropical regions we admire, the basic substrate is often referred to by ecologists simply as "fine, white sand" in most scientific papers- typically, but not necessarily a silica of some sort. And of course, other locations have slightly larger grain sizes of other pulverized stones and such. Still others are comprised of sediments which wash down from higher elevations during seasonal rains.

Deep rivers will typically have different substrate compositions than say, marginal streams or floodplain lakes, or even flooded forests. In the Amazon region, a huge percentage of the sediment and materials which comprise the substrates are from the Andes mountains, where they are transported down into the lower elevations by water flow.

This has huge foundational impact on the chemistry of the waters in the region. This process builds the fertile floodplain soils along Andean tributaries and the main stem of The Amazon.

As I mentioned before, there is a whole science around aquatic substrates and their morphology, formation, and accumulation- I don't pretend to know an iota about it other than skimming Marine biology/hydrology books and papers from time to time.

However, merely exploring the information available in scientific literature about  the tropical aquatic habitats we love so much- even just looking long and hard at some good underwater pics of them- can give us some good ideas!

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.

That's pretty much what we expect, right? Of course, there is more..and there are factors which impact both the composition and appearance of substrate.

First off, in some areas- particularly streams which run through rain forests and such, the substrates are often simply a soil of some sort. A finer, darker-colored sediment or soil is not uncommon. It's based on the ionic, mineral, and physical concentrations of materials that are dissolved into the water. And it varies based on water velocities and other factors, as touched on above. 

Meandering lowland rivers maintain their sediment loads by continually re-suspending and depositing materials within their channels- a key point when we consider how these materials stay in the aquatic ecosystems.

Okay, I could go on and on with my amateur, highly un-scientific review of substrates in Amazonia and elsewhere, but you get the point!

There is more to the substrate materials found in Nature than just "sand." That's the biggest takeaway here! So, as hobbyists, we have more options and inspiration to to draw on to create more compelling substrates in our aquariums!

What that means to us is (taking into account the "pasta sauce analogy", of course) is that we should consider mixing other materials into our basic aquarium sands. For example, you could mix aquatic plant soils into your sand. You could experiment with materials such as clay, or other mineral/plant-based components of varying particle sizes. 

Obviously, your substrate will look a lot different than the "typical" aquarium substrate when you start mixing materials. Your overall aquarium will, too. And that's a good thing, IMHO. I played around with this a lot in my office brackish water Mangrove aquarium, where the substrate played an integral functional role in the aquarium, as well as an aesthetic one...

You'll have to accept stuff like tinted water, turbidity, and "texture" within the aquarium.

We talk a lot about a concept that we call "substrate enhancement" or "enrichment" in the context of botanicals (we tend to use the two terms interchangeably). We're not talking about "enrichment" in the same context as say, planted aquarium people, with materials put into the substrate specifically for the benefit of plants.

Rather, "enrichment" in our context refers to the addition of botanical materials for creating a more natural-appearing, natural-functioning substrate- one which provides a haven for microbial life, as well as for small crustaceans, biofilms, fungal growths, and even algae, to serve as a foraging area for our fishes and invertebrates. 

There is something oddly compelling to me about both aquariums and natural biotopes with a diverse, interesting bottom structure.

Rather than simply "the bottom of the tank", I see the substrate as this magical place which fuels all sorts of processes within our aquariums, supporting higher life forms- and that Nature tends to it in the most effective and judicious manner possible.

Substrates in Nature- and aquariums-are diverse harbors of life, ranging from fungal and biofilm mats, to algae, to epiphytic plants. Decomposing leaves, seed pods, and tree branches prepare the substrate to recruit a complex web of life which helps the fishes we're so fascinated by to flourish.

And, if you look at them objectively and carefully, they are beautiful.

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.

It's not some amazing "revolution"- it's simply an evolution of practices that we've been playing with peripherally for decades in the hobby. It's a way of looking at what's already working and trying to figure out the "whys" as we go. 

Think beyond just sands...or anything resembling "conventional" aquarium substrate. Think about what goes on in the benthic (bottom) regions in the natural habitats we love, and what benefits or support the materials which aggregate there provide for the organisms within the ecosystem.

Understand that the substrate is a dynamic, extremely important part of the aquarium, too. And what we construct our substrate with, and how we manage it, is of profound importance to our fishes!

A combination of finely crushed leaves, bits of botanicals, small twigs, etc.within the sand can form the basis for a more "biologically active" and even productive substrate. As these materials break down, they are colonized by fungi and biofilms, and impart  tannins, lignin, and other sources of carbon into the water to fuel a variety of microbial growth.


And of course, larger crustaceans and even fishes will consume the organisms which live in this "matrix", as well as possibly consuming some of the detritus from the decomposing leaves themselves. This is precisely what happens in natural aquatic ecosystems.

Because of the very "operating system" of our tanks, which features decomposing leaves, botanicals, soils, roots, etc., we are able to create a remarkably rich and complex population of creatures within them.

Let's take advantage this!

This is one of the most interesting aspects of a botanical-method aquarium: We have the opportunity to create an aquatic microcosm-on many levels- which provides not only unique aesthetics- it provides some supplemental nutritional value for our fishes, and perhaps most important- nutrient processing- a self-generating population of creatures that compliment, indeed, create the biodiversity in our systems on a more-or-less continuous basis.


Most of our substrates will simply look different.

They'll have a variegated, sediment-laden, even "dusty"-looking appearance. Something very different from the fine, white sand that we typically see in aquariums. Adding mixes of materials to our substrates creates an entirely different form and function.

Yes, there is something incredibly beautiful and useful about utilizing these alternative materials in our substrates. They have created an incredible opportunity for us as hobbyists to forge new directions in the hobby. To embrace function first, and let the aesthetics unfold as a result.

And most important- to appreciate the wonders of Nature as it is- and how these systems organize themselves into beautiful, highly unique aquariums if we let them...


This is a huge point; something which everyone who works with botanical method aquariums comes to know and usually accept. We need to have an attitude which doesn't allow us to panic; to make fast, short-term moves in favor of longer-term outcomes. It's a very different philosophy. You need to accept different aesthetics. You need flexibility. You may even have to accept short-term losses for a greater long-term good.

You need to have faith in Nature.

It's a dance. An art form. A process, and an evolution. Sometimes seemingly chaotic, other times maddeningly slow. Always alluring. Always deferring to Nature...

And it's all held together by you- the aquarist, applying as much emotion as you do procedure- all done in the proper the right cadence.

Observe. Study. Learn. Share...Evolve...

...and Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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