Elevating the bottom...Another look at the evolving art and science of "substrate enrichment"

Okay, that was a weird title, huh? Almost sounds a bit obscene; however...it's not what you think!

I'm really into aquarium substrates.

LIke, obsessively so.

Specifically, creating substrates that are a reasonable representation of the bottom of habitats as diverse and unique as streams, ponds, temporal pools, peat bogs, and igarapes, as found in the tropical regions of the world. Each one of these habitats has some unique characteristics, and each one presents an interesting creative challenge for the intrepid hobbyist. Until quite recently, the most common materials we had to work with when attempting to replicate these substrates were sand, natural and colored gravels, and clay-comprised planted aquarium substrates.

And, since, as mentioned above, I'm a bit obsessed with substrates, that's why we offer a variety of other materials into your botanical-style aquarium substrate! 

If you're truly adventurous, this opens up a lot of cool possibilities for interesting functional and beautiful tanks. The bottom itself becomes a big part of the aesthetic focus of the aquarium, with the botanicals mixed into, or becoming the substrate- the world opens up!

These materials form an attractive, texturally varied "microscape" of their own, creating color, biodiversity, and interest. In fact, I dare say that one of the next frontiers in our niche would be an aquarium which is just substrate materials, without any "vertical relief" provide by wood or rocks.

Well, that's just me, of course... 🤓

Scientists have identified a number of different soil classes throughout the world. In the Amazonian region, a type of soil known as "Podzol" is associated with with black water rivers and lakes. "Podzols" are 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. Now, this makes a certain degree of sense, right, because we've long been told how "nutrient poor" blackwater systems are, and it starts with the substrate, right?

Even though it's nothing like the super fertile "garden forests" we imagine, there is a lot of terrestrial vegetation over this soil.  Locally called Varrillal which translates to “land of twigs”, it's a "stunted" forest, comprised of abundant thin, relatively short trees. A significant "root mat" covers the soils, and it's thought that most of the nutrient exchange must occur in this root mat, which keeps the remaining nutrients held within the system- hence the low nutrient levels. And it's another explanation for the relatively nutrient poor water in blackwater systems, right? The terrestrial plants are "hogging" all of the good stuff! (what little of it there is, anyways)

And then there are the aesthetics...

If you've seen pictures and videos taken underwater in tropical streams (again, I'm pulling heavily from the Amazonian region), you'll note that there is a lot of loose, soil-like material over a harder mud/sand substrate. Obviously, using an entirely mud-based substrate in an aquarium, although technically possible- will result in a yucky mess whenever you disturb the material during routine maintenance and other tasks. You'd need to "cap" it with more substantial materials to hold it in place. Anyone who's done a "mudded substrate" planted aquarium knows this!

So, how does the "tinter" create a more interesting, functionally aesthetic substrate in the aquarium?

Well, you could start with a thin layer of aquarium-grade sand, and build from there. I am a big fan of some of the finer sand materials, such as CaribSea's "Sunset Gold." This substrate , IMHO, faithfully represents (in appearanc,e) the podzol-comprised materials found in Amazonian regions. 

You could mix in stuff like our "Fundo Tropical", a course coconut-based material, or its counterpart, "Substrato Fino" (a very fine-grained version). These materials  have the added advantage of staying "down" nicely once you prepare them for use (boiling is the preferred method). They also last a very long time, becoming essentially inert after they releases their initial tannins into the water column. The intricate "matrix" it forms will become a very useful foraging area for many fishes, hosting small benthic life forms, just like natural stream bottoms do.

To this milieu, you could add materials like our "Mixed Leaf Media", a mix of several types of crushed tropical leaves, or "bits and pieces" of stuff like catappa bark, oak twigs, etc. These have that "functional aesthetic" benefit of looking very natural, while simultaneously imparting tannins and supporting the aforementioned life forms.

That's a lot of decomposing stuff, huh?

"Hey, Scott. Your proposing that I add a shitload of stuff that may trap detritus, uneaten food, solid fish waste, etc.- and some of it will break down in the process! Sounds like a recipe for a lot of debris in the system!" 

(Oh, just say it- you wanted to tell me it's a maintenance liability and sort of a mess if you're not meticulous and diligent in maintaining it). It's important to have adequate water movement, creation, and overall good husbandry when attempting such a substrate.

Well, yeah.

This kind of combination of natural materials can create a potentially messy substrate area if you are not a careful feeder, over-stock your aquarium, and tend to let things go. So, just be conscientious about maintenance!

That being said, I've found that, much like in nature, the materials that we place on the bottom of the aquarium will become an active, integral part of the ecosystem. From a "functional" standpoint, bottoms comprised entirely of, or supplemented with a variety of botanical materials form a sort of "in-tank refugium", which allows small aquatic crustaceans, fungi, and other microorganisms to multiply and provide supplemental food for the aquarium, as we've touched on before.

Stability and ease of maintenance are the (surprising?) benefits of such an enriched substrate, in my experience! 

It's certainly no stretch to call our use of botanicals as a form of "active substrate", much like the use of clays, mineral additives, soils, etc. in planted aquariums. Although our emphasis is on creating specific water conditions, fostering the growth of microorganisms and fungi, as well as creating unique aesthetics, versus the "more traditional" substrate materials fostering conditions specifically for plant growth.

About the most I could hope for in a quick piece like this is to pique your interest in taking a fresh look at the substrates that we typically give little to no "play."

I hope I've done that!

Let's see some experiments. Let's see some cool-looking 'scapes which aesthetically AND functionally represent the unique tropical substrates which form a highly important part of the fascinating ecosystems we love so much!

Stay innovative. Stay dedicated. Stay curious. Stay excited. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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