A most persistent myth...

One of the things I love most about the whole blackwater/botanical-style aquarium "genre" is that, even though hobbyists have been playing with them for decades, there has been virtually no discussion or serious analysis of the techniques, characteristics, and process involved in creating and maintaining them short of "Throw some peat moss in your filter..." (1960's-1980's) or, "Toss in 5 catappa leaves for every 10 gallons of water" (1990's-2,000's).

I mean, sure- in all fairness, there have been some articles and such from time to time about blackwater aquariums, but no real serious, consistent discussions of them. And in something as broad-reaching as the aquarium hobby, limited discussions on a topic generally leads to three possible things happening, in my experience:

1) Assumptions and long-held beliefs and misconceptions are perpetuated/regurgitated- often by those who have little, if any experience with the subject.

2) Only the bad experiences, warnings, and negative aspects of the topic are given play among hobbyists. "Myths" become  a major part of the narrative.

3) The topic becomes an arcane "sideshow specialty", garnering little interest while maintaining its aura of mystery and the persistent assertions that it's challenging and foolhardy to work with.

That's what happened with blackwater aquariums, for sure!

We've covered this before a few times, but for some reason, the myth persists that adding catappa leaves and pods and other botanical materials will create instant nature-like conditions in your hard, alkaline, city tap water.

It's a myth.

Oh, now sure, tannins and humic substances are imparted to water, even hard, alkaline water. Even in brackish water. So, yeah, it looks all dark and tinted, even though the pH and hardness might be quite high.

That's a different subject for another time, but you get the idea. Looks are only just that- looks! We can't get too caught up in the superficial aesthetics of tinted water and overlook the contributing factors and function.

So, why can you have dark, rich-looking water and still have it be hard and alkaline?

To understand why, we need to all re-familiarize ourselves with the concept of carbonate hardness.

Now, before we get too far, I'll dispense with the obligatory disclosure/confessional that my knowledge of water chemistry is quite basic, and I'm not preferring that anything discussed here is the "last word" on the subject. It's an explanation of some facts and ideas based on my limited college chemistry, and understanding of these things from being a practicing aquarist.

I admit that, at a certain point in the discussion about this stuff with really knowledgable people, my eyes start to glaze over...There are plenty of you out here who could "school me" on this stuff, and I encourage your input on these more esoteric, yet very important aspects of the hobby.

We will all benefit.

Ahh, back to that bit on carbonate hardness...

This is one of those terms, along with "general hardness" (GH), that we see bandied about all over the internet and in books and hobby discussions...It's super-confusing to me, as there are multiple ways of determining the hardness of water (in general, but for us, it's for aquarium purposes).

"Hardness", is essentially a measure of the total concentration of specific minerals dissolved in the water, including calcium and magnesium, as well as other minerals like potassium and sodium. It is said that the concentration of these minerals in a given quantity of water contribute to the "hardness."

There are a few ways of measuring this.

As a reef hobbyist, I was long ago indoctrinated to utilize KH (from the German word "karbonate") to measure the carbonate and bicarbonate ions in a given aquatic system, which function as "buffers", and keep the pH from dropping. And KH is a component of GH, to make matters more confusing (KH can never be higher than the "general hardness" of the water because of this fact). And a lot of test kits will measure both...as if a guy like myself needs more confusion in his life...

The easiest way to make "hard" water "soft" for us fish geeks is to invest in a reverse osmosis/deionization unit (RO/DI unit). This gives you water with little to no (ideally) general hardness, setting the stage to more easily reduce the ph utilizing botanicals and such. In general, it's fairly safe (gulp) to state that soft water is usually acidic, and "hard" water is usually alkaline.

And of course, that's where the fun (and confusion) begins!

A lot of people ask about utilizing leaves and other botanicals to lower the pH in their aquariums. It's a good question, and one worth addressing. As you are no doubt aware by now, many of these natural materials release substances such as  tannic and humic acids into the water, which can acidify it- IF the water has a low enough KH.

I'll say it again:

Most botanicals won't do much to significantly reduce the pH if you start with hard, alkaline water, as the KH will prevent the acids released by these materials from reducing the pH. 

As many of you know, it is entirely possible to have darkly tinted water that is hard and alkaline. Although the humic substances and tannins imparted by botanicals are present in water with those characteristics, it's a big difference between the water being a certain visual color and it being soft and acidic. 

I get a bit frustrated with the idea of commercial "blackwater extracts" creating a  sort of "instant" Amazonian type of water or whatever. I get frustrated because, although these products definitely work at tinting the water- and possibly even lowering the pH under the circumstances outlined above (water with little to no carbonate hardness)- they tend to perpetuate the myth that you can "just add a bit of this and a pinch of that" to your tap water, and you'll have a blackwater aquarium that will make your Neon Tetras spawn, or whatever.

If it were that easy, we'd have all been keeping blackwater tanks and spawning Rummynoses and the like really easily decades ago.

There is way more to it than that. 

Blackwater environments are a result of many factors, ranging from the geology of the surrounding soils to the composition of the materials which accumulate in the streams and rivers, or inundated forest floors.

Our practice of utilizing botanicals to achieve a more dynamic blackwater environment is not an exact science, either. Rather, it's an art form- a nuance, if you will- and it has its own set of guidelines, effects, and limitations. Creating a botanical-style, blackwater aquarium is not even as easy as tossing in some seed pods and leaves into a tank filled with RO/DI water, either.

Rather, it's an amalgamation of a number of different practices. You need to consider the overall aquatic environment that you're contemplating. You have to think about things like the influence of rocks, substrates, etc. You need to study how these dynamic habitats exist in nature, beyond just their dramatic and alluring appearance.

If only it was so easy, right? 

On the other hand, the fact that you need to learn a few things and understand the challenges and limitations imposed by Nature in order to achieve the desired conditions tells us that this is as much an "art" as it is a "science." Filled with nuance and observation and a certain amount of "going with our gut."

And that is the beauty of this blackwater/botanical-style aquarium stuff that we are so obsessed with. If it were just about adding a certain amount of "this or that" to our tanks and calling it a day, we'd see blackwater aquariums in every home that has fish. 

We still might get there. However, we'll get there by experimenting, observing, and sharing our experiences with other hobbyists. By not looking for "shortcuts" or "hacks." We'll get there by good, old-fashioned work. And by dispelling "myths", assumptions, and misconceptions with facts and a body of work that informs, inspires, and excites other hobbyists.

What could be more fun than that?

Stay curious. Stay excited. Stay interested. Stay bold. Stay diligent....

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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