Catappa leaves, botanicals, and the stuff they can- and can't do!

In todays internet-fuled hobby, the misconceptions- good and bad- about utilizing leaves and botanicals in our aquariums continue. And they spread really quickly! 

There is a lot of "stuff" out there ascribing capabilities and attributes to botanicals that simply isn't true. Stuff about how they impact water parameters in our aquariums. There is much confusion. Yes, you can use botanicals to influence the pH of your water if the carbonate hardness is minimal. They can and will impart humic substances and tannins into the water.

They will, of course, color the water. How much and to what extent is something that is simply unpredictable. 

Much like the misconception that botanicals soften the water, it was often assumed by hobbyists that the brownish tint imparted to the water by leaves and botanicals somehow implied that it is "soft and acidic." It does not.

Yes, some of these materials contain substances that can reduce the pH in water which has low to negligible carbonate hardness. 

However, the tannins, which are the substances which tint the water, cannot "overcome" the Calcium and Magnesium ions, and drive down the pH significantly in water with high levels of these carbonate hardness present. It simply is putting more materials into the water (which are often detectible by TDS meters in aquariums). And, as we've discussed before, there are natural habitats, such as the Tapajos in Brazil, which have essentially clear water, yet are rather soft and acidic. 

Color of the water is not a reliable indicator of pH.

First off, without delving too far into basic water chemistry, which I have neither the desire or ability to explain in simple terms, I think everyone needs to kind of delve into google and refresh (or educate for the first time!) themselves on the concepts of carbonate hardness and pH. This will set you up well for understanding exactly what these parameters mean, and how they can impact your fishes.

Suffice it too say, botanicals cannot influence the carbonate hardness of the water! They cannot "soften" it. Soft water is water that contains low concentrations of ions- particularly calcium and magnesium. In order to achieve "soft water", these ions need to be removed from the water. 

In Nature, soft water occurs where rainfall accumulates and rivers and streams are formed over hard, impervious, calcium-poor rocks. Geology, as we've discussed before, is a HUGE influencer of the carbonate hardness of the water in wild ecosystems (and in aquariums, for that matter!). For our purposes, the process of "ion exchange" is the most efficient way to soften water for aquarium use. And that is easily achieved by utilizing an RO/DI ("reverse osmosis/deionization) unit, of which dozens are available for hobbyist use!

For a detailed explanation of THAT process, just google it! My head spins just thinking of how to explain it in a non-confusing matter. In my opinion, an RO/DI unit is one of the fundamental investments that any serious botanical-style aquarium enthusiast should make. Yeah, they're a couple hundred U.S. dollars to start, and arguments could be made about their efficiency, etc., but if you really want to create optimum conditions for fishes requiring soft, acidic water, for most of us it's the best way to go. 

For those of you who have naturally soft water where you live, Mazel Tov. You'e probably stoked! Awesome. However, for the rest of us, we need to buy a damn RO/DI unit and be done with it. 🤓

Let's focus on leaves for a few minutes...Catappa leaves, specifically.

The "great catappa leaf exaggeration"- Part 500:  It has been known for many years by science that catappa leaves (and others) have substances in their tissues which do have some potential medicinal functions, like saponins, phytosterols, punicalagins, etc.  Fancy names that sound really cool- these are often bounced around on hobby sites as the "magic elixir" for a variety of fish ailments and maladies.

Now, I can't entirely beat the crap out of this idea, as these compounds are known to provide certain health benefits in humans. and for a long time, it was anecdotically assumed that they did the same for fishes. And believe it or not, there have been studies that show benefits to fishes imparted by substances in catappa and other leaves.

I stumbled across a study conducted in Thailand with Tilapia concluded  that Catappa extract was useful at eradicating the nasty exoparasite, Trichodina, and the growth of a couple of strains of Aeromonas hydrophila was also inhibited by dosing Catappa leaf extract at a concentration of 0.5 mg/ml and up. In addition, this solution was shown to reduce the fungal infection in Tilapia eggs!

And it is now widely accepted by science that humic substances (such as those present in botanicals) are thought to have a wide range of health benefits for fishes in all types of habitats. We've covered this before in a great guest blog by Vince Dollar, and the implications for the hobby and industry are profound. Although they are not the "cure all" that many vendors have touted them as, many leaves and other botanicals do possess a wide range of substances which can have significantly beneficial impact on fish health.

And, as a guy who sells leaves for a living, I've had to be careful to not ascribe miraculous attributes to the stuff I sell- because it's not only not helpful- it can be downright misleading and certainly counterproductive for the hobby and industry by doing so!

And I see a lot of counterproductive garbage being put out there at scale. It's important to address some of this stuff from time to time, especially when it's about our use of botanicals in natural-style aquariums. We have an obligation, of sorts, to elevate our practice of utilizing natural materials in aquariums, and that often means diving just a bit deeper when seemingly "too good to be true" assertions are made.

I'll say it ONE MORE TIME:

Catappa leaves cannot "cure fish diseases."

This is one which has been perpetuated for years (often by people who sell leaves online and elsewhere -hey, I'm in that group, huh? Yikes! 😳 ).

This assertion bothers the shit out of me.

Although, it actually has some validity to it, as outlined above. I said "some"- because we in the hobby and industry tend to selectively "cherry pick" stuff we like from science and run with that, often overlooking some of the more sobering realities in favor of the "sizzle."


That's where the danger of "regurgitation" sneaks in.

Those benefits that various leaves like catappa allegedly bring? Well, many of them are benefits ascribed to humans. And for a long time, it was anecdotally assumed that they did the same for fishes. Now, sure, humans aren't fishes, as we all know...Yet, I'll say it once more: There have been studies that show benefits to fishes imparted by substances in Catappa and other leaves.

Although they are not the "cure all" that many vendors have touted them as, leaves and other botanicals do possess a wide range of substances which can have significantly beneficial impact on fish health.


The practice of using catappa leaves in aquariums is quite old.

And there is a certain logic to their use, which is hard to question. For many years, Betta breeders and other enthusiasts in Southeast Asia added catappa leaves to the tanks and containers that held their fishes, and noticed a lot of positives…Those who actually fought their fishes seemed to feel that, when kept in water into which catappa had been steeped, their fishes recovered more quickly from their injuries. Those who simply kept fishes (not for “blood sport”) noticed increased overall vigor, appetite, and health among their fishes. 


Anecdotal? Perhaps.I mean, probably...

However, one thing I've learned about the early aquarists is that they employed very keen power of observation. They were a practical lot, if nothing more, who didn't have the internet and cool gadgets and stuff to rely on for information. It was more about trying stuff and going with things that seemed to work for them. They were obviously seeing something- or a combination of things, which led them to believe that using catappa leaves was beneficial to their fishes.

Now, this makes a lot of sense, right?

I mean, the natural habitats of many of the fishes of Southeast Asia are blackwater, botanical-influenced waters, rich with tannin from decomposing vegetation and naturally occurring peat.

As discussed above, many of the humic substances and compounds which benefit fishes are found in these natural waters.

As Catappa leaves and other botanical materials break down in our aquariums, they impart some of these beneficial compounds into the water, fostering a more healthy environment for fishes which are accustomed to blackwater conditions. Perhaps they perform an almost "prophylactic" role at preventing disease and supporting overall fish health, as opposed to functioning as some sort of "cure all." 

And that leads to more questions, of course:

What "dosage" do we apply? How many leaves steeped in how much water yields a concentrated solution of 0.5 mg/ml or more? How long do these materials need to be in the aquarium to accomplish this? And is there truly some measure of effectiveness, besides simply seeing your fishes happy and healthy?

We're learning the answers to some of these questions together. Catappa keeps calling...Botanicals keep beckoning.

Breaking through the barrier of assumptions, hyperbole, and fluff that has often clouded this tinted world before we all came together and made a real effort to understand the function as well as the aesthetics of this dynamic, engrossing hobby niche. 

It's on all of us- hobbyists, vendors, and lovers of aquairumstpo push forward and share the facts as they are, along with our personal experiences- to help move the "state of the art" forward.

Stay curious. Stay resourceful. Stay diligent. Stay bold. Stay creative...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


1 Response

Sheila Edmonds
Sheila Edmonds

May 08, 2024

I am considering purchasing some but after reading this article is it true that I should only use with blackish aquarium or natural aquarium? I’ve got angelfish that is constantly under attack with Parasites which I’ve treated. Some advised that I should add to my aquarium for them. What do you think? I’d appreciate your advice!

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