Bouncing off the bottom...The idea of "substrate enrichment" beckons...My continuing substrate obsession...

When it comes to substrates in our aquariums, there are so many choices these days. We have specialized planted aquarium substrates, purely decorative choices, and...and...

Okay, we have those two at the moment.

Yet, don't get me wrong...I LOVE aquarium substrates. I'm practically as obsessed with substrates as you are with rocks or driftwood! Like, weirdly obsessed... Like, I'm the guy who hangs out for uncomfortably long times at the Carib-Sea or Seachem booths at conferences and trade shows, talking it up with the beleaguered sales reps, which just want the day to end, and for this weird guy to stop talking about their products...

Yeah, geeky. 

Like, I'd only sell aquarium substrates if that was a thing. I love them. I think about them a lot. 

Maybe too much!

And soon, we'll have some more truly "functional aesthetic" substrate choices available. In the mean time, you could be adventurous and concoct your own.

Yeah, I've always looked substrate materials the way other people look at cocktails: It's about mixing stuff.

Yeah, seriously. 

Now, in Nature, there are numerous factors which contribute to the composition of substrates in wild aquatic habitats, 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.

So, why the @#$%&* do we as hobbyists, who want to create the most realistic approximations of wild habitats possible, just "mail it in" when it comes to substrate? I mean, just open a bag of _____________ sand or whatever, and call it a day and move on to he more "exciting" parts of our tank?

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

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.

However, IMHO, they are a great "starting point" for creating more dynamic substrates 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?


(Damn, it's 7:00AM here in L.A., and now I'm craving Penne...WTF?)

There, in a nutshell, is my theory of aquarium substrates. 

We can do a bit better.

Now, in many of the tropical regions we admire, the basic substrate is often referred to 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.

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 on 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!

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 such, 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 you 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're taking something that's typically just sort of "there"  in most aquairums, and making it a lot more interesting- elevating it as an important structural/functional aesthetic component of the aquarium.

And of course, you can experiment with botanical materials!

Yeah, when we first started Tannin Aquatics over 4 years ago, I made it a point to offer you materials which I felt played a key role in what I call "habitat enrichment"- an entirely concocted and decidedly un-scientific way of saying that adding botanical materials into the typical inert substrate materials we use will foster enhanced biological activity. You know, like decomposition, the development of fungi and biofilms, and the the creation of more dynamic areas for fishes to forage among.

Materials such as our "Mixed Leaf Media", which is a combination of finely crushed leaves, 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.

Its a very different looking- and functioning- substrate, for sure. At the risk of sounding too commercial here, suffice it to say, we have a whole damn section on our site called "Substrate Additives" for the very purpose of facilitating such geeky experiments! 

This stuff is THAT interesting to me...It's wide open for lots of experimentations, evolutions, and even breakthroughs.

Look to Nature, again.

Bold experiments and efforts, based on what we see in the wild aquatic habitats of the world. Amazing stuff.

And of course, those types of things require some "trade offs", right?

Yeah, I KNOW that our aquairums are NOT open systems like the wild habitats, and that the dynamics of weather, water input/throughput, etc. are vastly different...However, that doesn't preclude us from trying to replicate- on some levels, the function of these structures as we see them in Nature, does it?

Of course not. You just need to accept some stuff.

You'll have to get used to stringy biofilms. You will see detritus and decomposition. By mixing materials such as "MLM" , "Fundo Tropical", and "Substrate Fino", just to name a few into your sand, you can create a very interesting- one might, to borrow a term from our vivarium friends, call "bioactive" substrate! 

You will also possibly create a bit of a mess if you're not too fastidious about the overall husbandry. You need to not overstock, overfeed, etc. Basic stuff. Sure, it's entirely possible to create a smelly, anaerobic pile of shit on the bottom of your aquarium! You need to move forward with cation. You need to observe very carefully, have reasonable expectations about what will happen, and you have to accept an entirely different look. 

Typically, when "enriching" your substrate with botanical materials, you'll see an initial "surge" of the aforementioned biofilms and such, ultimately subsiding to a sort of "baseline" of a little bit of stuff in and among the substrate. WARNING: It will NEVER look "pristine" or "competition sterile." Get that idea out of your head immediately.

However, it WILL look much, MUCH more natural, dynamic, and altogether unique. When you're incorporate decomposing botanical materials, not only are you adding to the biological load of the aquarium, you will be fostering the growth of beneficial microorganisms, like bacteria...Could this lead to enhanced denitrification or even "fermentation" in deeper substrates, which enhance the overall water quality? And what about it's potential as a "mulch" of sorts for aquatic plant growth?

Are there a lot of benefits to playing with these ideas?

I have evidence to make me believe so...

Mainly, undetectable levels of nitrate and phosphate on advanced hobby-level test know, overall good water quality. I've maintained these types of substrates over very long periods of time without any issues. Period. You may nuke your entire f--king tank, of course, if you're not careful- but I think it highly unlikely if you follow basic tenants of aquarium husbandry, otherwise! I've played with this idea for almost 15 years without a single issue.

"Gee Scott- thanks! Another way to kill my fishes, courtesy of your weird ideas!"

Okay, it's not that weird. And really, not that dangerous. I just don't want some flat-out beginner, heading home from the LFS with a brand new nano-sized aquarium, complete with a "Sponge Bob" bubbling ornament, purple gravel, and 20 Neon Tetras to go online, find our site, see some pics, and dump 12 ounces of crushed leaves into the gravel and expect some sort of miracles, you know?

So, yeah. Radical ideas require some education and understanding, mindset shifts, managed expectations, and responsibility.

And observation and patience, too. 

Yet, the possibilities are too exciting NOT to venture into this area! 

The idea of "enriching" your aquarium substrate is compelling, especially when we look at it from a more "holistic" perspective of a botanical-style aquarium. It becomes yet another component of the microcosm we create. And of course, it needs to be viewed as a dynamic part of the aquarium's ecology- not simply as an "aquascaping prop" for a tank.

You've seen me playing with the "Urban Igapo" idea and the funky substrates for the better part of a year now, and soon, we'll bring some stuff out for you to try!

In the mean time, please just think about this stuff more...

Think about the process and what goes on in such a substrate. Study it. Observe it.

And reap the potential benefits when it's done right.

Stay bold. Stay creative. Stay observant. Stay vigilant. Stay diligent. Stay patient...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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