The dark, deep, yet exciting side of botanical-style aquariums...Caveats, challenges..rewards!

With all of the interesting experiments and new aquariums we've seen springing up using botanicals to achieve interesting aesthetic and functional results in blackwater aquariums, it's always nice to look into things which can be challenging or of concern from time to time.

For no particular reason, I just felt like discussing a topic or two today which focuses on creating safe, beneficial habitats for our fishes. No particular event or events triggered this, other than the desire to continuously create an honest, frank dialogue among members of "Tint Nation" to objectively look at the good, the bad., and even the ugly side of our "practice." 

As always, I'm constantly "iterating", or in our language, "evolving" my aquariums to embrace new ideas, concepts, or aesthetics which I think would push the "state of the art" of blackwater/botanical-style aquarium down the road a bit. Lately, I've been thinking about an even more realistic-looking-and functioning- "flooded forest" themed aquarium, something we're seeing more and more of our community playing with. And I've been thinking through further refinements of the "deep botanical bed"/sand substrate relationship. I've been spending a lot of time researching the natural systems and contemplating how we can translate some of this stuff into our closed system aquaria.

One of the things that many hobbyists ponder when we contemplate deep botanical beds consisting of leaves, sand, and other botanical materials is the buildup of hydrogen sulfide, CO2, and other undesirable compounds within the substrate.

Well, it does make sense that if you have a large amount of decomposing material in an aquarium, that some of these compounds are going to accumulate in heavily-"active" substrates. Now, the big "bogeyman" that we all seem to zero in on in our "sum of all fears" scenarios is hydrogen sulfide, which results from bacterial breakdown of organic matter in the total absence of oxygen.

Let's think about this for a second.

In a botanical bed with materials placed on the substrate, or loosely mixed into the top layers, will it all "pack down" enough to the point where there is a complete lack of oxygen and we develop a significant amount of this reviled compound in our tanks? I think that we're more likely to see some oxygen in this layer of materials, and I can't help but speculate- and it IS just speculation- that actual de-nitirifcation (nitrate reduction), which lowers nitrates while producing free nitrogen, might actually be able to occur in a "deep botanical" bed.

And it's certainly possible to have denitrification without dangerous hydrogen sulfide levels. As long as even very small amounts of oxygen and nitrates can penetrate into the substrate this will not become an issue for most systems. I have yet to see a botanical-style aquarium where the material has become so "compacted" as to appear to have no circulation whatsoever within the botanical layer. Now, I base this on visual inspection of numerous tanks, and the basic chemical tests I've run on my systems under a variety of circumstances.

And then there's the question of nitrate.

Quite honestly, even in the most heavily-botanical-laden systems I've played with, I have personally never seen a higher nitrate reading than around 5ppm. I attribute this to good quality source water (RO/DI), careful stocking, feeding, good circulation, and consistent basic aquarium husbandry practices (water changes, filter maintenance, etc.). Now, that's just me. I'm no scientist, certainly not a chemist, but I have a basic understanding of maintaining a healthy nitrogen cycle in the aquarium. And I am habitual-perhaps even obsessive- about consistent maintenance.

I think the very few issues that we've seen with people "pushing it too far" in terms of botanical applications were caused by rapid influxes of large quantities of botanical materials, which (this is theory) overwhelmed the resident bacterial population and might have resulted in rapid oxygen depletion and a corresponding increase in CO2. The result was fishes hanging at the surface in an attempt to get oxygen. Almost every situation like this I heard of was remedied in a relatively short period of time by adding additional aeration into the tank and/or removing some of the materials.

Generally, loss of life was minimal (that's an awful term, though) or nonexistent as a result of these measures. Regardless, it's really important to be careful. Fish can die if we push it too hard.  It's not just "Boil, dump...Instant Amazon..."  Measured experimentation is required. We're adding biological materials to established aquariums, which might not be able to handle large, fast influxes.

There's obviously some "upper limit" of how much botanical material we can add to a given system in a brief period of time, and it's especially more profound in newly-established aquariums with "immature" nutrient export mechanisms in place.

Typically, botanical-"powered" systems run trouble free, especially when you understand what's going on, know what to expect (yeah, decomposing leaves, biofilms, etc.), and have mechanisms in place to accommodate them.

Now, this is not to say that you can't have some disasters if you "go too hard" or "too fast" with lots of botanicals in a closed system. It just makes sense, right? You're adding material which will decompose in the water, and if adequate nutrient export systems are not in place to deal with it, you could have some problems. This isn't some new revelation; it's something we've been talking about here for a long time. And it's common sense- "Aquarium-Keeping 101", really. However, it's important to bring up the potential "dark sides" of botanical-style aquariums now and again, as more and more hobbyists start experimenting with this stuff.

Throwing light on the dark side...

What kinds of things can we do to prevent problems like this?

Well, for one thing, we can add botanical materials gradually, at a slow, steady pace. This will give our bacteria population a chance to catch up with the influx of materials being added. Also, it will slow down the pace of any pH variations (assuming we are utilizing stuff that can lower the pH in our tanks) so that the fishes can adjust to them.

It's common sense "best practice" for us.

Another thing would be to employ good circulation within your system, which not only results in greater oxygenation and "mixing" of water "strata" - it physically suspends fine particulates in your system as well, making it easier for mechanical filtration to remove (of course, that assumes you don't like the look of "stuff" in the water, as some of us do!).

Relatively shallow sand beds seem to be optimal for identification, and many of us employ them for the aesthetics as well. Light "vacuuming" of the top layers to remove any potential "dead spots" is always a good practice, IMHO. Any debris stirred up can easily be removed mechanically by filtration, as mentioned above.

While we're on the subject of filters, some form of mechanical (ie' filter pads, etc.) and chemical (like activated carbon, PolyFilter, ReNew, or other media) is highly recommended.

Many fellow "Tinters" are surprised to know that I utilize some form of chemical filtration media on a full-time basis in all of my blackwater and brackish, botanical-style systems, and have for years. As we've discussed for a couple of years now, having these filter media in place is an "extra layer of protection", and any perceived "tint removal" that you might experience as a result of using them is far outweighed by the benefits.

Besides- have you looked at the color of the water in my tanks lately? Plenty dark.


Follow our instructions on the preparation of aquatic botanicals.  Yes, some of our ideas on steeping catappa leaves or whatever before use might seem ridiculously conservative. However, recommend some of these procedures because we have a responsibility to share techniques that we fill will yield the best possible outcomes for the largest number of customers. Some of you do add leaves directly to your tanks, and have experienced no issues. I have played with that too, and have never had a problem, but I still recommend at least a rinse or steep for some leaves, to remove surface pollutants and other organics possibly bound up in the dermal layer of the leaves. Plus, a "steep" of some sort helps buoyant leaves saturate and sink faster, if nothing else. 

And then there is the use of aquatic plants; something that we are seeing more and more of in botanical-oriented systems. In terms of impact on the substrate, it's a known fact that plants remove ammonia directly, and typically will prevent the anaerobic conditions that promote production of hydrogen sulfide within the substrate itself. So there are many benefits to including them in our botanical-style blackwater aquariums!

The simple practice of adding "botanical stuff" into our aquariums is not some "high concept thing." However, the impacts on the water chemistry and overall aquatic environment- not to mention, on our fishes- are profound, fascinating, and real! Being careful and taking the time to clean, prepare, and add botanicals to your aquarium in a measured manner always yields a better outcome. Going slowly also gives you the opportunity to address any issues that you might have before they become critical.

It just makes sense to be patient.

Now, some 2-plus years in, I think many of you in our customer base "get it", and understand that we need to look at the addition of botanicals to our systems as a big ongoing "experiment", with some "best practices" having emerged fairly quickly, and others having been developed as we as a community gain more experience with this stuff. Being responsible stewards of our little closed aquatic habitats just goes with the territory. And perhaps most important, everyone seems to realize that with each aquarium they set up, and with every experiment or idea they implement, the "state of the art" of this type of methodology is improved, refined, and perfected.

Everyone who participates has valuable experience that they can share. There is still plenty to do, many potential breakthroughs to be had, techniques to perfect, mistakes to be made, science to interpret, and- unfortunately- occasional tragedies to learn from. 

We as an enthusiastic and engaged global community have slowly and carefully taken the concept of a blackwater, botanical-style aquarium out of the realm of "carnival side show" into an evolving, legitimate practice to achieve significant results with our treasured fishes. We continuously see reports of dramatic fish health improvements, spawnings of delicate species, seen wonderful, realistic representations of nature, even experienced an occasional tragedy or two on very rare occasions...and realized from each- that we learn.

 And we recognize that we are all part of a greater whole, and that the world we're doing will benefit the generations of aquarists who will follow us, and apply what we're learning in ways that we probably haven't even contemplated yet.

Thanks for coming along for the ride!

Stay generous. Stay open-minded. Stay careful. Stay patient.

And Stay Wet.


Scott Fellman

Tannin Aquatics

Scott Fellman
Scott Fellman


Leave a comment