The color of water...

One of the most common misconceptions about botanical-method aquariums is that they must absolutely be filled with deeply tinted water and replete with fungal-and-biofilm-encrusted decomposing leaves, twigs and seed pods.

Remember, this is a methodology, not a "style of aquascaping", and the reality is that you can have an aquarium which fully embraces the ecological aspects of natural aquatic systems and have clear, slightly tinted, or even turbid water. It's not a "prerequisite" to have that dark brown water. Quite honestly, we see the tinted water as a "collateral" aesthetic benefit of embracing this approach- not the main reason to do it. 

The hobby has somehow latched on to the most superficial aspect of blackwater- the look- and in the social media landscape, the appearance of blackwater has led to a tremendous confusion about what it actually is.

As we've mentioned hundreds of times here, the aquairum definition of "blackwater" seems to apply to any tank which has less than crystal-clear, blue-white water. Remember, in Nature, the term "blackwater" applies to water with a very specific set of chemical characteristics; the color of the water is a result of the presence of various compounds in the water. The visuals may play a huge role in our "interpretation" of what we think "blackwater" is- but the reality is that it's much more of a "chemical soup" which makes it so.

Although the three "classical water types" (white, black and clear) are used by science to describe many of these habitats, aquarists tend to classify water as "blackwater" or "clearwater", which, although not scientifically "pure", tends to make our understanding and discussions easier!

And the reality is that there are many, many habitats throughout the world which have tons (literally) of botanical materials in them, yet have relatively clear water. It's certainly not a given that the presence of leaves, wood, and other botanical materials in a given body of water will result in brown water and low pH. Rivers like the Juruá, Japurá, Purus, and Madeira) are turbid, with water transparency that varies, and they transport large amounts of nutrient-rich sediments from The Andes. Their waters have near- neutral pH and relatively high concentrations of dissolved solids.

The Rio Xingu and Tapajós are classic examples of "clearwater" rivers. One of the largest tributaries of the Amazon, the "Xingu" has an abundance of rock, and a higher content of dissolved minerals than a blackwater habitat like the Rio Negro. There is not much suspended matter because the rock formations which the river courses through are ancient and no longer erode in the current. The pH varies between 6 and 7.

And, for almost as long as hobbyists have been playing around with "blackwater aquairums", 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 understand the most simple of questions- like, what exactly is “blackwater”, anyways?

A scientist 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 SiO2contents. Tannins are 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 “black-water.” 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 black waters typically arise from highly leached tropical environments where most of the soluble elements 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 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.

Interestingly, however, these waters are surprisingly low in dissolved organic compounds (DOC). In fact, Rio Negro black waters are theorized to have low DOC concentrations because of thdiluting effect of significant amounts of rainfall, and because they are diluted by clear waters from nearby systems low in dissolved organic compounds.

Sort of  self-regulating, to an extent, right?

In the podzolic soil where blackwater originates, most of the of the extractable substances in the surface litter layer are humic acids, typically coming from decaying plant material. Scientists have concluded that greater input of plant litter leads to greater input of humic substances into ground water.

In other words, those leaves that accumulate on the substrate are putting out significant amounts of humic acids, as we've talked about previously! And although humic substances, like fulvic acid, are found in both blackwater and clear water habitats, the organic detritus (you know, from leaves and such) in blackwater contains more extractable fulvic acid than in clearwater habitats, as one might suspect!

The Rio Negro, for example, contains mostly humic acids, indicating that suspended sediment selectively adsorbs humic acids from black water.  The low concentration of suspended sediments in rivers like the Rio Negro is one of the main reasons why high concentrations of humic acids are maintained. With little to no suspended sediment, there is no "adsorbent surface" (other than the substrate of the river, upon which these acids can be taken hold of (adsorb).

When you think about it, all of this this kind of contributes to why blackwater has the color that it does, too. Blackwater in the Amazon basin is colored reddish-brown. Why? Well, it has  those organic compounds dissolved in it, of course. And most light absorbtion is in the blue region of the spectrum, and the water is almost transparent to red light, which explains the red coloration of the water!

As we've mentioned many times, water color, although helpful to us aquarists in some respects, is not an absolutely reliable indicator of the pH or ionic composition of the water! There is no substitute for good, old-fashioned water testing!

Remember, just because the water in a botanical-influenced aquarium system is brownish, or has a bit of noticeable "turbidity", it doesn't mean that it's of low quality, or "dirty", as we're inclined to say.  I can't stress it often enough. It simply means that tannins, humic acids, and other substances are leaching into the water, creating a characteristic color that some of us geeks find rather attractive. If you're still concerned, monitor the water quality...perform a nitrate test; look at the health of your animals.


Interestingly (and perhaps, confusingly) the lower section of some Amazonian black-water rivers such as the Rio Negro, Tefé, Uatumã and Urubu in Brazil; Nanay in Peru and some streams in Colombia can have ionic composition and/or pH-values similar to the white water rivers, and not like the typical Amazonian blackwater rivers. It is though by researchers that low electrical conductivity values can be responsible for this phenomenon. 

In addition, it's though that many rivers and streams have to be considered as “mixed waters” resulting from the influence of tributaries with different physical and chemical properties of their waters.

As if we don't need more confusion, right? Talk about "muddy waters!"

So, for us aquarists, the arguments and discussions can rage on and on and on, and aquarists who have been to various parts of these rivers may observe somewhat different characteristics than others...and be 100% accurate in their findings! Generalizations, although often a "no- no", may actually be useful to us. (gulp)

One of the big discussion points we have in our world is about the color and "clarity" of the water in our blackwater aquariums. We receive a significant amount of correspondence from customers who are curious how much "stuff" it takes to color up their water.

Those of us in the community of blackwater, botanical-method aquarists seek out tint and "body" in our water...while the rest of the aquatic world- well, they just sort of... freak the fuck out about that, huh?

Our aesthetic "upbringing" in the hobby seems to push us towards "crystal clear water", regardless of whether or not it's "tinted" or not. And think about it: You can have absolutely horrifically toxic levels of ammonia, dissolved heavy metals, etc. in water that is "invisible", and have perfectly beautiful parameters in water that is heavily tinted and even a bit turbid.

(FYI, WIkipedia defines "turbidity" in part as, "...the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air.")

That's why the aquarium "mythology" which suggested that blackwater aquairums, or aquariums with tinted water were somehow "dirtier" than "blue water" tanks used to drive me crazy. The term "blackwater" describes a number of things; however, it's not a measure of the "cleanliness" of the water in an aquarium, is it?


Color alone is not indicative of water quality for aquarium purposes, nor is "turbidity." Sure, by municipal drinking water standards, color and clarity are important, and can indicate a number of potential issues...But we're not talking about drinking water here, are we?

No, we aren't! 

(And yes, aquariums with high quantities of organic materials breaking down in the water column add to the biological load of the tank, requiring diligent management. This is not shocking news. Frankly, I find it rather amusing when someone tells me that what we do as a community is "reckless", and that our tanks look "dirty."

As if we don't see that or understand why our tanks look the way they do.)

There is a difference between "color" and "clarity."

The color is, as you know, a product of tannins leaching into the water from wood, soils, and botanicals, and typically is not "cloudy." It' actually one of the most natural-looking water conditions around, as water influenced by soils, woods, leaves, etc. is ubiquitous around the world. Other than having that undeniable color,there is little that differentiates this water from so-called "crystal clear" water to the naked eye.

Of course, the water may have a lower pH and general hardness, but these factors have no bearing on the color or visual clarity of the water. And conversely, dark brown water isn't always soft and acidic. You can have very hard, alkaline water that, based on our hobby biases, looks like it should be soft and acid. Color is NO indicator of pH or hardness! Again, it's one of those things where we ascribe some sort of characteristics to the water based solely on its appearance.

As I've mentioned before, a funny by-product of our more recent obsession with blackwater aquariums in the hobby is a concern about the "tint" of the water, and yeah, perhaps even the "flavor" of said water! A by-product of our acceptance of natural influences on the water, and a desire to see a more realistic representation of certain aquatic environments.  

And that means that dark water we love so much.

Yeah, we now see posts and discussions by hobbyists lamenting the fact that their aquarium water is not "tinted" enough. A lot of hobbyists have "bought in" to those mental shifts we keep talking about...

You sort of have to smile a bit, right?

Total mental shift, huh?

We impart color-producing tannins into the water in our aquariums by utilizing leaves and other botanical materials, like seed pods, cones, bark, and even wood. Confusingly, you can achieve the look of blackwater habitats even with relatively hard, alkaline water. Of course, there is more than just the aesthetics, right? Many of these materials will also impart complex compounds, like polyphenols, polysaccharides, lignin, and other substances into the water as well, which can have positive influences on fish health, and the overall aquarium environment. 


So, the approach to create “aquarium quality” blackwater is surprisingly simple, really. Start with high quality RO/DO water, add some botanical materials like leaves, bark or seed pods, and in theory, you’ve created the aquarium equivalent of “blackwater.”  I mean, it’s not quite that simple, as the easy process belies the complex chemical interactions that take place in the water to create these conditions, but for most of us, that’s kind of how it works on a superficial level.

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-method 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. 

And of course, it's perfectly okay and easy to have an aquarium filled with all of these  tannin-producing materials and to render the water crystal clear with activated carbon or other chemical filtration media! 

And understanding the interactions of these materials with water and the overall aquatic environment in our tanks AND in Nature, have enormous implications for the future of our hobby. 

Water is a sort of "blank canvas"- a starting point...a "media" for our work. So many possibilities...That's the allure of water! 

The beauty of an aquarium is that you can either remove or contribute to the color and clarity characteristics of your water if you don't like 'em, by simply utilizing technique- ie; mechanical and chemical filtration, water changes, etc.

The color of water. It's that simple.

Stay engaged. Stay curious. Stay observant. Stay thoughtful...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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