Does your "blackwater aquarium" truly contain "blackwater?" A "case study" in hobby responsibility.

We interrupt our blissful ignorance for a cold whack upside the head...

Do we have something wrong here? 

Seemingly out of nowhere, the idea of creating a deep, dark, mysterious "blackwater aquarium" utilizing botanical materials has become a sort of “thing.” Now, in all fairness, hobbyists have been experimenting with blackwater aquariums for decades.

Yet, I wonder if what we call "blackwater" squares with the ecological description of what it really is, and what characteristics define it.

"Shit, there he goes...!"

I like emphasizing the phrase "botanical-style" aquarium even more than the term "blackwater aquarium", although I have used the two sort of together over the years. 

No one can argue that what we play with in our little hobby niche is NOT a "botanical-style aquairum"- there is little to dispute that.

The whole concept of utilizing these materials to create not only healthy  environments for our fishes, but to create aesthetically fascinating, remarkably faithful functional replications of wild habitats is being given some new life.

It's been amazing so far.

Yet, are these "blackwater aquariums?"

Or, do we just use the term "generically" to describe our love of tinted, tannin-stained water? Regardless, it's an unusual sector of the hobby where a lot of people are starting to play...

The idea of blackwater aquariums, or at least, aquariums with deeply tinted water being seen as a "side show" curiosity is falling by the wayside, as hobbyists are utilizing these types of tanks to keep even fishes which have been with us for decades, and achieving remarkable results...and discovering a new aesthetic and enjoyment in the process. 

And, for almost as long as hobbyists have been playing around with them, there has been confusion, fear, misunderstanding, and downright misinformation on almost every aspect of them! We’re still seeing a lot of that confusion.

It’s important to really try to understand the most simple of questions- like, what exactly is “blackwater”, anyways?

A scientist or ecologist will tell you that blackwater is created by draining from older rocks and soils (in Amazonia, look up the “Guyana Shield”), which result in dissolved fulvic and humic substances, present small amounts of suspended sediment, and characterized by lower pH (4.0 to 6.0) and dissolved elements, yet higher SiOcontents. Magnesium, Sodium, Potassium, and Calcium concentrations are typically very low in blackwater. Electrical conductivity (ORP) is also lower than in so-called "whitewater" habitats.

Tannins are also imparted into the water by leaves and other botanical materials which accumulate in these habitats.


The action of water upon fallen leaves and other botanical-derived materials leaches various compounds out of them, creating the deep tint that many of us are so familiar with. Indeed, this leaching process is analogous to boiling leaves for tea. The leached compounds are both organic and inorganic, and include things like tannin, carbohydrates, organic acids, pectic compounds, minerals, growth hormones, alkaloids, and phenolic compounds.

In summary, natural "blackwaters" typically arise from highly leached tropical environments where most of the soluble elements in the surrounding rocks and soils are rapidly removed by heavy rainfall. Materials such as soils are the primary influence on the composition of blackwater.

Leaves and other materials contribute to the process and appearance in Nature, but are NOT the primary “drivers” of its creation and composition.


So, right from the start, it’s evident that natural blackwater is “all about the soils…” Yeah, it’s more a product of geology than just about anything else. 

More confusing, recent studies have found that most of the acidity in black waters can be attributed to dissolved organic substances, and not to dissolved carbonic acid. In other words, organic acids from compounds found in soil and decomposing plant material, as opposed to inorganic sources. Blackwaters are almost always characterized by high percentages of organic acids.

Knowing what we now know from science, does a "blackwater aquarium" as we call it it really contain "blackwater?" Or is this another case of the aquarium hobby running with the easiest definition and basing it off of aesthetics over everything else? You know- the water is dark and tinted, and it looks different than clear water,'ve got a "blackwater aquarium", right?

Well, you can have stupidly hard, alkaline (and even brackish!) water and have a definite brownish tint, imparted by tannins from leaves and such. Is THAT "blackwater?"

Well, in the aquarium hobby it might be. But not to a scientist. However, we don't run our tanks to please the scientific community, right? They're supposed to be for our enjoyment. Yet, Nature has rules and characteristics that are unavoidable, which define and influence things, wether we like them or not.

I use straight-up, reverse osmosis, deionized water in my tanks, use weird clay/sediment substrates, and add lots of leaves and botanicals to my tanks. The water is generally darkly tinted, and the pH tends to run in the "mid sixes"; carbonate hardness is minimal. 

Is it "blackwater?"

Not by the strict ecological definition. I mean, it has SOME characteristics of natural blackwater, but it's not exact. It's a representation of blackwater characteristics.

Splitting hairs? 


Remember, again-blackwater habitats in Nature are strongly influenced by geology.

As aquarists, we tend to over-emphasize the role of leaves and botanicals in creating “blackwater”, because we approach things a bit differently than Nature does.  In an aquarium, we can use a slightly different techniques and materials to achievef the same, or similar results as Nature does.

Again, that's okay.

It starts by utilizing water with little to no carbonate hardness (that’s sort of equivalent to what you get in Nature when the water drains over those weathered rocks and soils).

Yet, if you embrace the scientific description of blackwater based on its chemical/ionic composition, you just have" tannin-stained water", with lower pH and hardness.

NOT "blackwater", by the strict ecological definition, right?

It's a "semantics thing", isn't it? 


And I do understand that it's probably not THAT big a deal. However, it IS important for us to not delude ourselves into thinking that just tossing some leaves into an aquarium and admiring the tinted color gives us a "blackwater aquarium," like you see in a lot of the so-called "influencer" videos on social media that pop up regularly now. Just sort of "mailing it in" by touching on the most superficial aspects of the concept.

If we throw around ideas like, "The tank in this video represents a blackwater river in Amazonia" or some other such grandiose pronouncement, we owe it to our audience to either try to explain what this means, what the characteristics of a natural blackwater habitat are, or why our tank, filled with lots aquatic plants, gravel, a few leaves, and water of unspecified chemical characteristics isn't "blackwater." It perhaps, superficially, mimics some aspects of the blackwater environment. It's "inspired by..."

But that's it.

And that's okay, but we have a responsibility to our fellow hobbyists to explain this.

To NOT be more accurate in our description about what we do in this sector-to just "cliche" it and label any tank with tinted water a "blackwater aquarium" runs the risk of simply "dumbing down" what we do, and working against the efforts and progress made by so many hobbyists to create a proper, replicable, and consistent methodology to creating botanical-style aquariums.  And it displays a fundamental ignorance of the work of many researchers and scientists, who help classify and study these habitats.

Botanical-style aquariums. Tanks which incorporate botanical materials to influence some aspects of the water chemistry and biology. That's what we play with. Many times, the result is an aquarium with water that has a brownish tint, perhaps a slightly reduced pH, and an array of decomposing leaves and seed pods. 

It's a methodology to create more natural functioning aquariums. It just happens to result in aquariums which look different- perhaps, superficially like blackwater habitats. 

So yeah, there's that.

I mean, there is no grand, omnipotent "aquarium terminology and standards committee" that is responsible for assuring that a set of agreed upon standards applies in order for an aquarium to be classified as a "backwater aquarium", or whatever. Rather, it's the collective responsibility of all of us who play with tanks that seek to replicate this environment to educate ourselves about natural blackwater habitats, and to not convince ourselves and others that we are working with something that is a precise replication of them. 

Seems like I'm really harping on an issue that is not all that important, right? I beg to differ...Not because I'm trying to be an arrogant jerk, shitting on everyone who throws a specific label on their work. It's not because I know everything (I sure as hell don't!). It's because we are at an important inflection point in hobby history, where the superficial can easily overtake the substantial- simply because it's easier to say whatever, and because fewer and fewer hobbyists seem to be inclined to research stuff or themselves, relying on "that guy online" or wherever to be the ultimate "authority" on whatever he or she is producing a video about.

Damn, I keep coming back to this stuff, don't I? Because I think it's really important that we hold ourselves accountable, It's what will keep the hobby healthy and thriving for years to come.

So, does your "blackwater aquarium" actually contain "blackwater?"

Likely not, at least by the generally agreed-upon ecological description used by scientists. However, by the standards which many in the hobby use to define "blackwater"- it just might be. And that's not a bad thing, of course. Perhaps the qualifiers "blackwater inspired", or "aquarium-hobby-defined blackwater" would be admittedly clunky, yet reasonably appropriate descriptors to use.

Perhaps not.

Does it matter? 

Well, it matters if we are convincing ourselves that we have something that we don't, and if we make dogmatic statements based largely on assumptions. And it matters most of all, to our fishes, whose very lives depend on the quality and diligence we apply to our work.

Regardless, we need to enjoy it for what it is, strive to refine and improve it if it's not what we want, and to understand and share what we do have as accurately and honestly as possible.

Like so many things in nature, the complexity of blackwater habitats is more than what meets the eye. Chemically, biologically, and ecologically, blackwater habitats are a weave of interdependencies- with soil, water, and surrounding forest all functioning together to influence the lives of the fishes which reside within them.

No single factor could provide all of the necessary components for fish populations to thrive. To damage or destroy any one of them could spell disaster for the fishes- and the ecosystem which supports them. It is therefore incumbent upon us to understand, protect, and cherish these precious habitats, for the benefit of future generations. 

Yes, blackwater aquariums have started to move out of their long-held status of "side show" and onto the "main stage" of the freshwater aquarium hobby- attracting new hobbyists not only with their unique aesthetics- but with the promise of tangible benefits for the fishes which we love so much.

It goes way beyond the unique aesthetics. It's about ecology. Function. Process.

And, like so many things in the hobby, patience, understanding, and responsibility are some of the most valuable "ingredients" for success.

Stay diligent. Stay observant. Stay creative. Stay honest. Stay responsible...

And Stay Wet.


Scott Fellman

Tannin Aquatics 











Scott Fellman
Scott Fellman


1 Response


January 23, 2024

I’m thrilled that in my searching to understand “Blackwater” aquariums and if it’s something I would like to try, this is the first thing I read. Thanks for the interesting read and inthe information points to research.

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