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The concept of "substrate enrichment"- a freshwater refugium, or just an accumulation of "stuff?"

Tannin Aquatics

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One of our most popular products is our "substrate enrichment media", called "Fundo Misto."


The coconut-based product has a course texture and size which, when mixed with more "conventional" sands and gravels, helps create a tannin-producing, environment-enriching, and aesthetically pleasing alternative to "basic" substrates in your aquarium. 

We began offering this product because, several years back, I became fascinated with the idea of creating more interesting, biologically diverse substrates in natural aquariums. Other than in planted systems, which use special blends of nutritive soils and materials, little attention has been paid in the hobby to creating "active", interesting substrates for general aquarium use. Sure, there were some increasingly more available sands and gravels of various sizes and colors- a great start. However, I couldn't find anything else on the market that would help replicate natural stream or river substrates to any great extent.


There seemed to be a gap between what substrates are really like in nature, and our overly-generalized, sort of "deconstructed" concept of what they should be like in the aquarium. Like in many areas of the hobby, I believe we became set in our ways; perhaps, even a bit fearful of trying things that were different. In the shrimp-keeping world, there is justifiable concern about trying things that can affect environmental stability and water quality, which I always understood- particularly coming from a "reef keeping" background, which makes the shrimp-keeping world seem very laid back by comparison! 

Regardless, concern over incorporating a melange of potentially environment-affecting stuff in our shrimp tanks is valid. 


Some of this might be for perfectly rational reasons: Our aquarium are not open rivers and streams. They are closed systems, which, although they incur similar processes to those occurring in nature, are not the same. Aquarists tend to shy away from anything that seems to create a potentially difficult-to-manage system. And let's face it- not everyone likes the look of lots of "stuff" on the bottom of their aquarium!

Although, speaking from a shrimper's perspective, I can't help but notice the sort of "inconsistency" that we often have in our thinking: We fear any sort of environmental changes in our systems, yet we casually throw in everything from sweet potatoes to nettles, to Turkish Hazel as "foods", yet these materials will often linger in our systems for days-even longer- obviously breaking down in our aquariums, and we pay them little mind. What do these things do? Granted, you're talking about small quantities, but conceptually, it's kind of the same, right? So I proceeded to experiment with "substrate enrichment" in both my fish and shrimp systems, and I can truly state that I've never experienced any health issues with any of my animals that can be attributable to the use of these materials in my systems. 

But that's me, of course. 


Regardless, my decades of reef aquarium keeping, and the philosophy of embracing the processes and diversity natural systems, left me surprisingly fearless and eager to experiment. For many years, reef aquariums incorporated the concept of a "refugium"- a protected place within the aquarium system, where animals and plants that would otherwise be a part of someone's daily meal before they had a chance to multiply, could thrive and help enrich the overall environment. 


I realized that, although perfectly legitimate and functional, the execution of a typical refugium in the marine sense involves hardware, such as a separate aquarium, to foster the diversity, which can add to the complexity and expense of a typical aquarium system, often unnecessarily, IMHO. Also, in our case, the primary goal is to establish the substrate as an area of foraging, nutrient processing, and shelter, perhaps more than it is to provide an area for supplemental food sources (i.e; aquatic crustaceans) to multiply, as in a marine system; nonetheless, the concept is valid. 


Wouldn't it make more sense to somehow incorporate a "refugium-like" area within the confines of the aquarium itself? Preferably, one which is both aesthetic AND functional, and incorporates simple, inexpensive natural materials? Of course! And what better place to accomplish this than "on the bottom" of our tanks- an area more-or-less neglected in freshwater aquarium keeping for a century or more!


Natural streams, lakes, and rivers typically have substrates comprised of materials of multiple "grades", including fine, medium, and coarse materials, such as pebbles, gravels, silty clays and sands. In the aquarium, we seem to have embraced the idea of a homogenous particle size for our substrates for many years. Now, don't get me wrong- it's aesthetically just fine, and works great. However, it's not always the most interesting to look at, nor is it necessarily the most biologically diverse are of the aquarium.


A lot of natural stream bottoms are complimented with aggregations of other materials like leaf litter, branches, roots, and other decomposing plant matter, creating a dynamic, loose-appearing substrate, with lots of potential for biological benefits. Of course, we need to understand the implications of creating such "dynamic" substrates in our closed aquariums.


Obviously, in the aquarium, high levels of decomposing plant material can create water quality management and oxygenation challenges, particularly in small tanks, so, although we embrace the natural processes, for sound management, it's better to replicate the composition and appearance with materials that don't decompose so quickly. Otherwise, we could just dump a bunch of decomposing plant stuff into our aquariums and call it a day! 

Enter the aquatic botanicals.


By incorporating a selection of aquatic botanicals, such as the aforementioned "Fundo Misto", Catappa leaves, and other, more durable items, like banana stems pieces, coco curls, and the like, you are simulating the aesthetics- and to an extent- the function- of a natural stream bed...Without the potential dangers of managing rapidly decomposing, water-quality-challenging processes in a closed system.


Over the long term, this substrate will perform slightly differently than what you're used to in an aquarium. You'll see some accumulation of detritus, a matrix of algae, and perhaps some aquatic crustaceans as well. Some of the materials, such as leaves, will decompose more quickly than others, requiring replacement. In an otherwise well-managed system, water quality will be unaffected, save the pH influence and visual "tint" from the materials used. Although water quality will be high, the appearance of the substrate will not be the scrupulously-clean, almost "sterile" appearance that we're used to in aquariums. Rather, you'll see a more natural-appearing, fascinating appearance.


In addition to providing a great natural aesthetic, such a substrate will provide foraging opportunities for many fishes, as well as shelter, spawning sites, and a "nursery" for many fishes-and shrimps- that would otherwise be subject to predation in a more conventional "open" substrate. 


By employing this idea of "substrate enrichment", you're taking an otherwise "humdrum" region of the aquarium (the bottom!) and fostering a biologically active, aesthetically pleasing microcosm within the aquarium that would typically be overlooked. 


We think that's worthy of your consideration! This is not "the bee's knees"; not the end-all and do-all for everything- but we think it's worth examining as a possibility for shrimp systems. Understandably, it is not for everyone. There is the chance it could fail miserably for you, although I believe it a small one, based on my results and those of other shrimpers who tried this stuff. There is certainly some risk with any experiment; any new concept.  Responsible experimentation is always a good thing.

Stay excited. Stay open-minded to the possibilities.

Stay Wet.

Scott Fellman

Tannin Aquatics





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