Learning, adjusting, tweaking...searching for "The Blackwater Recipe..."

Now closing in on three years in operation here at Tannin Aquatics, we're seeing a lot more experimentation and applications of botanicals in blackwater aquariums. And we are seeing a lot of hobbyists new to the concept starting to try this stuff.

Some of the most common questions we receive lately are "How much _______ do I need to get my water to look like________?" or "How much_______ is needed to lower the pH in my tank?" Or, "How much do I need to get a good amount of humic substances and tannins into my aquarium?"

I usually respond with a simple, "I don't know."

These are all really good questions. Logical. Important.  I kind of feel like many hobbyists are looking for a plug-and-play "formula" or "recipe" for how to accomplish certain water-conditioning tasks.

I totally get that. But the reality is...there IS no "recipe" for how to do this stuff.

And it sucks, I know.

Oh, first off- I don't see any way that you can take your hard, alkaline tap water, throw in a bunch of leaves and cones or whatever, and soften the water and drop the pH to Amazonian levels. Let's just take that off the table right now. That task requires a process of deionization, which I don't see happening by just using botanicals in tap water! If you want to significantly affect the pH of your water with botanicals, you need to start with RO/DI water, in my opinion and experience. 

Yet, we do have questions about altering the pH, etc. of our aquarium water with botanicals. 

And they are legitimate, IMHO. 

However, the problem, as I see it, in answering these common questions generically is that there are so many variables in the equation that it's almost impossible to give a definitive answer. Over the years, those vendors who sold catappa leaves, for example, would recommend starting amounts ("three leaves per 15 liters of water" or whatever...) of botanical materials to use in our aquariums. Now, this was all well and good, but it's based on....what? I mean, is this based on how many leaves of _______ size that a typical hobbyist with a 10 gallon aquarium needs to get the water looking brown? Or to lower tapwater with a starting pH of 7.4 and a KH of ___ to pH of 6.9? Or to impart "x" ppm of tannins or humic substances into this given quantity of water?


It falls apart from there. I cringe when I see seemingly authoritative recommendations from vendors (myself included, lol) about how much of what to add. It's really a matter of basing this on our own (and increasingly) your experience wth using botanicals to influence the pH and visual tint of the water.  (Oh, and remember, "tint" is not an indication of the pH or alkalinity...) And that's okay; we have to start somewhere. But I think that we need to be realistic with our expectations about what information we can glean from our experiments.

First off, there is no practical and easy "off the shelf" way, short of some pretty intense scientific testing on individual specimens of various botanicals- to know exactly how much of what color-producing and pH reducing tannins, humic substances, etc. are bound up in the tissues of a given botanical item. I mean, I am sure there is a legitimate way to test batches of leaves and botanicals of a specific size, for example, and come up with an average quantity (in what measure, I wouldn't be certain) of how much of "what" compounds are present.

There are ways to test for concentrations of tannin. For example, the "Stiasny method", in which "a 100 mg of sample tannins are dissolved in 10 ml distilled water. 1 ml of 10M HCl and 2 ml of 37% formaldehyde are added and the mixture heated under reflux for 30 min. The reaction mixture is filtered while hot through a sintered glass filter. The precipitate is washed with hot water (5x 10 ml) and dried over CaCl2. The yield of tannin is expressed as a percentage of the weight of the starting material." Straightforward for a scientist in a lab, exceedingly difficult for the average hobbyist. 

And what are you starting the test with? "Sample tannins" means what, in our context? Sounds discouraging, at first. Now, the good news is that there are actually test kits out there to do it. Hach, for example, makes a Tannin/Lignin test kit! And I think that will be a good starting point for many of those interested in finding out just what's going on in their aquarium. Knowing that you have a 20 US-gallon tank filled with RO/DI water, a non-buffering substrate, and "12 Magnolia leaves, 12 Catappa leaves of 3"-4", 12 Coco Curls of about 4" in size, and 20 small Alder cones"- or whatever, yielding a tannin reading of 15 mg/l of tannic acid in the water (or whatever) will at least help establish some sort of very crude, yet aquarium-relatable guidelines.

And we need a reference- a baseline comparison to natural waters, like the Rio Negro, Atabapo, etc. for these numbers to have any real meaning, IMHO. Sure, I have studied the water chemistry composition of some major blackwater rivers based on work done in scholarly research, and much of this data is based on things we could test for in the aquarium (like TDS, pH, dissolved metals, conductivity, etc.), but something like "tannic acid expressed as mg/l" is not something we've seen. Now, if some of my friends and colleagues who travel to regions like the Amazon and other blackwater habitats invest in one of these $160 tannin test kits, run some samples and record tests from various sites and at different times of the year, etc. we at least have a baseline for the concentrations of tannins in natural water- another target we can shoot for when trying to replicate natural conditions!

Of course, even knowing that, there are problems. First off, just knowing how much "tannins" are in natural water, although helpful, is simply a starting point. And if we did have numbers of how much of this stuff is bound up in the tissues of the various leaves, pods, etc., -while interesting to know- it's really not all that useful when we really don't have a guideline as to how much of what specific compound or compounds are needed to create the specific effects we are looking for in our aquariums! And of course, even knowing that- would this be based on how much of _______ you need to achieve a pH reduction or tannin/humic substance ppm of _______ in a given sample of RO/DI water with ____starting pH, TDS, and KH? Or...?

Oh, and being natural items, wouldn't the levels of these compounds within the leaf or seed pod tissues themselves vary from batch to batch, season to season, and be affected by preparation, age of the materials, how they are stored, etc. etc., etc?


Although there may even be breakthroughs in terms of backwater extracts and additives coming to market, there are still a lot of questions that would have to be answered before we could simply state that "X" drops per gallon of such an such a formula would yield a specific outcome. This reminds me of the reef aquarium world more an more, lol.

So, if I've made any "argument" here, it's that this stuff is every bit as much of an "art"- in terms of aquarium keeping- as it is a "science." We will, at least for the foreseeable future, have to use the data we have available and formulate a best guess as to how much of what can give us some of the impacts we are interested in for our aquariums. We simply can't authoritatively make blanket statements like, "You need to use "X" catappa leaves per gallon in order to recreate Rio Negro-like conditions in your aquarium!" Marketing hyperbole aside, we really are sort of...guessing.

And that's certainly nothing to be discouraged about!

We, as a community, are getting deeper into the functional aspects of blackwater, botanical-style aquariums than ever before. More light is being shed on what's going on in both our aquariums and in the natural habitats we desire to replicate. We are learning more every day about how the presence of tannins and humic substances in our aquariums is affecting the health, longevity, and spawning behaviors of our blackwater fishes. We're learning about the challenges and realities of managing blackwater systems over the long term- understanding the good, the bad, and the dangerous possibilities that are present when we experiment with these ideas.

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. And most important of all- this interest is throwing more and more attention to amazing wild habitats that we seek to emulate...and gives us all the more reason to protect, study, preserve, and treasure them for our children's children in centuries to come.

Yes, there is way more to this stuff than just tossing some leaves into your aquarium. Much more. There is no "recipe" for this stuff. Not yet, anyways. We're all still learning how to navigate this dark, compelling, fascinating aquatic world.

We're happy you're along for this never-ending voyage of aquatic discovery,

Stay curious. Stay bold. Stay excited. Stay engaged...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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