Talking dirty...again...

As you know, I spend an inordinate amount of time talking about sediments, mud, leaf litter, and soil, and how these materials play an important role in the aquatic ecosystems from which many of our favorite fishes come.

I mean, for the most part, we'd call this stuff "dirt."

And, as I discovered during my extensive summer "urban igapo" experiments, I think there is a lot to be gained from playing with "dirt" in our aquariums...Well, more accurately, terrestrial soils of various compositions.


Now, I know that the idea of "dirted" tanks is not at all new, particularly to the planted tank world. There is a whole fascinating "subculture" of planted people doing amazing things with "dirted" tanks. I enjoy reading about their almost rebellious simplistic approach. I love that attitude and these people. We've talked about them before here, but they really deserve some credit!

Part of me loves them because, at least to this outsider, they appear to be pissing off "the establishment" and their fancy gadgetry and snobbish approach. They're doing this complicated thing in such a simple matter that it draws criticism from the "experts", which is just badass. Now, they're utilizing garden soil and such, which is geared towards, well- growing stuff. 

What I'm talking about is utilizing soils of various types in tanks where plants are not the primary focus. Like, using it as part of an aesthetic and functional substrate. Where the impact of the material on the environment of the aquarium as a whole is more important than its ability to grow...plants. 

I'm talking about a fish-centric microcosm.

This is where I part ways with these bold rebels...

Yes, I'm thinking about "dirt"...or, really, soil-the stuff in your garden that get's kind of muddy when it gets wet. Would using this stuff in your substrate, either "solo" or as a "mix", be a cool way of capturing the "look and feel" of some of our blackwater habitats? Now, I realize it's  A LOT more complicated than just throwing some "dirt" into the water, and that the chemical compositions of many of the soils which originate in the tropical regions we attempt to replicate in our aquariums are often vastly different geologically from our North American/European soils.

Yet, I find it sort of intriguing to utilize "clean dirt" (shit, is THAT an oxymoron?) in a botanical-style, blackwater aquarium. 

This was probably one of the more reckless, least scientific ideas I've wanted to play with in a while...Or was it?

There is absolutely no basis for using "just any old dirt" in a blackwater, botanical-style aquarium- other than the fact that "dirt" is found in many of the streams and rivers of the world. Yet, I decided to "formulate" my own version of the soils found I the tropical areas I was interested in, utilizing the closest combinations of materials I could find to do the job...

And it was fun...and no fishes croaked or anything, so... 

(Not that "not croaking" is the measure of success during an aquarium experiment, but...)

There must be some benefits, right?

Of course...Let's dive deeper.

Sure, super alkaline soils or soils with a lot of salt or other mineral content will possibly wreak havoc on our attempts to create soft, acidic waters- but there must be some types of soils with some attributes that will perhaps release some beneficial trace elements and minerals into the water? Again, I AM NOT SUGGESTING THAT ANYONE DO THIS without a lot of consideration and forethought...but...

I'm merely sharing with you something I have play with a lot. I think there is something there...

I recall, a number of years back, I was working on an aquatic display project for a museum in museum Connecticut. We were growing riparian plants from the beaches of Long Island Sound, and I remember literally digging up clumps of these plants, along with the surrounding soil and mud, and utilizing them in an aquarium with local marine was an incredible display...Super simple, but cool- and the experience never quite left my head...I thought, "Why not do this with a tropical freshwater tank?" 

Or, perhaps, with brackish?

Taht made a lot of sense...

Now, with Estuary, our foray into brackish water aquairums, the idea of utilizing/recreating the muds and silts and leaves for substrate and as a huge part of the closed ecosystems and is the basis of our mangrove biotopes, and I can't help but let my mind return back to that "dirt thing" and the potentially interesting benefits (like the potential to impart trace elements, organics, etc. to the water) that could come from it.

Mixing muds and soils with dried mangrove leaves and some botanicals has been a very interesting long-term game! There is so much more to learn about utilizing this approach to "tinted" brackish-water aquariums. More to come, for sure!!!

I do remember taking a fair amount of shit from some of my friends for my "mud and leaf litter" approach to brackish, because, according to at least two fo them,  it seemed (wait for it...) contrarian to prevailing hobby wisdom about "cleanliness..."

Of course, right there, that made me want to do this even more!


Naturally, when it came time to wrap my head around freshwater soil/mud-influenced habitats, my brackish experience loomed large...Mud and dirt can and should be used in a variety of ways, besides just for planted least, that's my opinion and experience.

And I think we can work with this stuff to our fishes' advantage! And I think experimenting more with this stuff gives us the opportunity to recreate- on a more realistic level- some of the natural habitats that our fishes come from...specifically, seasonally inundated forest floors and grasslands..

Once again, we have a natural habitat which might not be everyone's idea of "beautiful" in the traditional sense. However, when "interpreted" in the context of aquariums, it becomes the basis for an engrossing, highly unusual, and altogether fascinating display!


We've talked about the idea of "flooding" an aquarium setup designed to replicate an Amazonian forest before. You know, sort of attempting to simulate some of the processes which happen seasonally in Nature. With the technology, materials, and information available to us today, the capability of creating a true "year-round" habitat simulation in the confines of an aquarium/vivarium setup has never been more attainable.

The time to play with this concept is now! It's really fun, trust me.

We've been testing the idea for a long time here, and have been formulating some soils which attempt to replicate some of the attributes of those found in these habitats during the "dry" season. I'm using materials like Kaolintic clays, sediments, iron-rich planted substrates, etc. in our "mixes."

And the stuff, when flooded, gives you an effect that's similar to what happens in the igapo.

Sure, the water gets cloudy for a bit.

The water is tinted, turbid, and sediment-laden. Eventually, it settles out. If you planted grasses and plants which are able to tolerate submersion for some period off their life cycle, they'll "hang on" for a while- until the waters recede. Just like in Nature.

To replicate this process is really not difficult. It mimics the "dry start" method that many aquatic plant enthusiasts play with. Except our goal isn't to start plants for a traditional aquarium. It's to replicate, on some levels, the year-round dynamic of the Amazonian forests.

We favor terrestrial plants- and grasses-grown from seed, to start the "cycle." I used readily available Paspalum grass (P. repens).  This genus (I believe P. notatum) is found in South America and is ubiquitous.

So, to make a long story short, the stuff grows!

To those of you who are ready to downplay the significance of experimenting with this stuff because "people have done 'dry start' planted tanks for years", take comfort in the fact that I fully recognize that, and acknowledge that we're taking a slightly different approach here, okay?

You'd need to create a technical means or set of procedures to gradually flood your "rainforest floor" in your tank, which could be accomplished manually, by simply pouring water into the vivarium over a series of days; or automatically, with solenoids controlling valves from a reservoir beneath the setup, or perhaps employing the "rain heads" that frog and herp people use in their systems. This is all very achievable, even for hobbyists like me with limited "DIY" skills.

I just gradually added water via a pyrex measuring cup and called it a victory for low tech...

You just have to innovate, and be willing to do a little busy work. You can keep it incredibly simple, and just utilize a small tank. Liek with every weird experiment we do, you must be patient, and willing to accept a failure or two along the way...

I've threatened to unleash my personal "soil formulation" to you guys in the near future, and it's really predicated upon me mixing the stuff up in larger quantities, now that I have a couple of "recipes" that work.

And of course, if I actually had access to clean podzolic soils, I can't help but  wonder what the ins and outs of using naturally collected stuff could be. 

I'm rambling. Not really fully developing the idea..Just sort of throwing out thoughts. It's an idea...sort of one of those "bring up to your fish geek friends and let them run with it" types...

Yet, soils and rocks and materials like these play a huge role in many of the "part-time terrestrial" habitats that we're so curious about replicating in our tanks.

And of course, it's a scientific fact that one of the most important influences on blackwater rivers is the geology- the soil and sedimentation of the surrounding areas. It starts with the soils. Blackwater rivers, like the Rio Negro, for example, originate in areas which are characterized by the presence of white sands known as "podzols." (note that, biotope-oriented aquascapers!)

Podzols are soils with whitish-grey color, bleached by organic acids. They typically occur in humid areas like the Rio Negro and in the northern upper Amazon Basin. And the Rio Negro and other blackwater rivers, which drain the pre-Cambrian "Guiana and Brazilian shields" of geology, can in part attribute the dark color of their waters to high concentrations of dissolved humic and fulvic acids!

Although they are the most infertile soils in Amazonia, much of the nutrients are extracted from the abundant plant growth that takes place in the very top soil layers, as virtually no plant roots are observed in the mineral soil itself.

One study I read concluded that the Rio Negro is a blackwater river in large part because the very low nutrient concentrations of the soils that drain into it have arisen as a result of "several cycles of weathering, erosion, and sedimentation." In other words, there's not a whole lot of minerals and nutrients left in the soils to dissolve into the water to any meaningful extent!

Hmm..nutrient concentrations, ionic composition and minerals and...this stuff is interesting.

Perhaps another reason (besides the previously cited limitation of light penetration) why aquatic plants are rather scare in these waters? Oh, and it would appear from studies I've stumbled upon, that that the bulk of the nutrients found in these blackwaters are likely dissolved into the aquatic environment by decomposing botanical materials, such as leaves, branches, etc.

Why does that sound so damn familiar?

Besides the color, of course, one of the defining characteristics of blackwater rivers is pH values in the range of 4-5, and low electrical conductivity. Dissolved minerals, such as  Ca, Mg, K, and Na are negligible. And with these low amounts of dissolved minerals come unique challenges for the animals who reside in these systems.

How do fishes survive and thrive in these rather extreme habitats?

It's long been known that fishes are well adapted to their natural habitats, particularly the more extreme ones. And this was borne out in a recent study of the Cardinal Tetra. Lab results suggest that humic substances in the water protect cardinal tetras in the soft, acidic environment in which they reside by preventing excessive sodium loss and stimulating calcium uptake to ensure proper homeostasis.

This is pretty extraordinary, as the humic substances found in blackwater actually enable the fishes to survive in this highly acidic water which is devoid of much mineral content typically needed for fishes to survive!

Oh, and this juicy finding in a study on humic substances in ornamental fish aquaculture really perked up my senses a bit:  "Humic substances are not real alternatives to strong traditional therapeutics. However, they show different advantages in repairing secondary, stress induced damages in fish."

Something in those leaves and botanicals, right?

Yeah, there is... And it goes hadn't in hand with soils, too...

The benefits of botanicals and soils go far beyond just the cool aesthetics they impart, too! Like, what we are doing with leaves, twigs, substrate materials, seed pods, etc. has a physiological impact on the fishes we keep. 

What a powerful incentive to study and enjoy both the aesthetics and environmental enhancement capabilities of the botanical materials we tend to be so obsessed with around here!

There's a lot to unpack. A lot to think about. Much to still learn and figure out. We as a community and global movement are off to a pretty good start, though! It's exciting to contemplate what's next!

Playing with "dirt" and all of the other botanical materials we've been publicly obsessing about for years here at Tannin is just the start of another evolution in the technique and practice of developing the ultimate in natural-style aquariums. Everyone can contribute the body of knowledge and help unlock potential breakthroughs.

And it all starts with simply acting on those "dirty" thoughts we have in our heads, right? 😆

Stay curious. Stay diligent. Stay patient. Stay daring. Stay excited. Stay creative...

And Stay Wet!


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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