Bringing up the biome...

There is a certain allure- a fascination...even obsession about considering our aquariums as little closed ecosystems, reacting to both internal and external inputs, stimuli, and environmental pressures.

When you think of aquariums in this manner, they become a whole lot less of a "pet holding container" and a lot more of a little slice of Nature that you're recreating in your home. And of course, the botanical-style aquarium is an expression of this thinking. A microcosm fully dependent upon botanical materials to impact fully effect the environment.

One of the aspects of utilizing botanicals in our aquariums that we discuss, but can't think about enough, is their importance to the "microbiome" of the aquarium environment.

A "microbiome", by definition, is defined as "...a community of microorganisms (such as bacteria, fungi, and viruses) that inhabit a particular environment." (according to Merriam-Webster)

Now, sure, every aquarium has a microbiome to a certain extent:

We have the beneficial bacteria which facilitate the nitrogen cycle, and play an indespensible role in the function of our little worlds. The botanical-style aquarium is no different; in fact, this is where I start wondering...It's the place where my basic high school and college elective-course biology falls away, and you get into more complex aspects of aquatic ecology in aquariums.

Yet, it's important to at least understand this concept as it can relate to aquariums. It's worth doing a bit of research and pondering. It'll educate you, challenge you, and make you a better overall aquarist. In this little blog, we can't possibly cover every aspect of this- but we can touch on a few points that are really fascinating and impactful.

An interesting place to start is to simply review a bit about the very composition of the materials that we play with, like seed pods and leaves and such, and how they interact with the aquatic environments that we've created.

Many seed pods and similar botanicals contain a substance known as lignin. Lignin is defined as a group of organic polymers which are essentially the structural materials which support the tissues of vascular plants. They are common in bark, wood, and yeah- seed pods, providing protection from rotting and structural rigidity.

In other words, they make seed pods kinda tough.

That being said, they are typically broken down by fungi and bacteria in aquatic environments. Inputs of terrestrial materials like leaf litter and seed pods into aquatic habitats can leach dissolved organic carbon (DOC), rich in lignin and cellulose. Factors like light intensity, mineral hardness, and the composition of the aforementioned bacterial /fungal community all affect the degree to which this material is broken down into its constituent parts in this environment.

Hmm...something we've kind of known for a while, right?

So, lignin is a major component of the "stuff" that's leached into our aquatic environments, along with that other big "player"- tannin.

Tannins, according to chemists, are a group of "astringent biomolecules" that bind to and precipitate proteins and other organic compounds. They're in almost every plant around, and are thought to play a role in protecting the plants from predation and potentially aid in their growth. As you might imagine, they are super-abundant in...leaves. In fact, it's thought that tannins comprise as much as 50% of the dry weight of leaves!


And of course, tannins in leaves, wood, soils, and plant materials tend to be highly water soluble, creating our beloved blackwater as they decompose. As the tannins leach into the water, they create that transparent, yet darkly-stained water we love so much!  

In simplified terms, blackwater tends to occur when the rate of "carbon fixation" (photosynthesis) and its partial decay to soluble organic acids exceeds its rate of complete decay to carbon dioxide (oxidation).

Chew on that for a bit...Try to really wrap your head around it...

And sometimes, the research you do on these topics can unlock some interesting tangential information which can be applied to our work in aquairums...

Interesting tidbit of information from science: For those of you weirdos who like using wood, leaves and such in your aquariums, but hate the brown water (yeah, there are a few of you)- you can add baking soda to the water that you soak your wood and such in to accelerate the leaching process, as more alkaline solutions tend to draw out tannic acid from wood than pH neutral or acidic water does. Or you can simply keep using your 8.4 pH tap water! 

"ARMCHAIR SPECULATION": This might be a good answer to why some people can't get the super dark tint they want for the long term...Based upon that model, if you have more alkaline water, those tannins are more quickly pulled out. So you might get an initial burst, but the color won't last all that long...

Interesting stuff, and all part of the little "stew" we make when we set up a botanical-style aquarium, right?

I think just having a bit more than a superficial understanding of the way botanicals and other materials interact with the aquatic environment, and how we can embrace and replicate these systems in our own aquariums is really important to the hobby. The real message here is to not be afraid of learning about seemingly complex chemical and biological nuances of blackwater systems, and to apply some of this knowledge to our aquatic practice.

Okay, let's think about the biology of these ecosystems for a bit, and contemplate how some aspects of their composition and function can be applied to our aquariums.

During the rainy season in the tropics, overflowing streams flood the rainforest floor, accumulating materials which the fish communities utilize for food and shelter. And materials which fall from the surrounding trees and banks are major contributors to the productivity of this ecosystem. As the waters recede somewhat, temporary streams flow through these areas. 

They become rich, complex ecosystems, bristling with life.

Interestingly, scientists have found that these streams have very little internal production of food sources for their resident fishes. Rather the food sources come from materials such as plants, fruits, leaves, and pieces of wood which come from the surrounding terrestrial environment.

Oh, and insects.

Lots of insects from the surrounding trees and "shorelines", which fall into the water.

These materials and organisms are known as "allochthonous inputs" in ecology- materials imported into an ecosystem from outside of it. This is rather interesting point. Essentially, it means that these areas, rich habitats that they are, are almost completely influenced by outside materials....

And, as one might expect- as more materials fall from the trees and surrounding dry areas, the greater the abundance of fishes and other aquatic animals which utilize them is found.

And materials will continue to fall into the water and accumulate throughout the periods of inundation, maintaining the richness of the habitat as others decompose or are acted on by the organisms residing in the water.

Not unlike an aquarium, right?

I mean, we need to get it in our heads that botanicals are "consumable" items, which need to be regularly replaced as they decompose, in order to maintain environmental consistency.

Yeah, it's the "jumping off point" for one of my favorite speculative areas in our little hobby speciality:

With botanicals breaking down in the aquarium as a result of the growth of fungi and microorganisms, I can't help but wonder if they perform, to some extent, a role in the management-or enhancement-of the nitrogen cycle.

In other words, does having a bunch of leaves and other botanical materials in the aquarium foster a larger population of these valuable organisms, capable of processing organics- thus creating a more stable, robust biological filtration capacity in the aquarium?

With a matrix of materials present, the bacteria (and their biofilms, as we've discussed a number of times here) have not only a "substrate" upon which to attach and colonize, but an "on board" food source which they can utilize as needed? Facultative bacteria, adaptable organisms which can use either dissolved oxygen or oxygen obtained from food materials such as sulfate or nitrate ions, would also be capable of switching to fermentation or anaerobic respiration if oxygen is absent.


We've talked about that before, right? And I'm not talking about this in regards to making kambocha, either!  Botanical "layers"- particularly, leaf litter beds- in the wild, offer an interesting study in nutrient processing and food production for the surrounding aquatic ecosystems. And, although botanicals accumulate to significant depth in some areas, the processes which we are fascinated with even occur at surprisingly shallow depths...

One study of wild leaf litter beds in Amazonia indicated that the majority of the aerobic decomposition probably occurs in the upper 10 cm of the leaf litter bed, as lower material is more tightly packed, reducing O2 diffusion, and is generally older and already well decomposed. It is also thought that fermentation processes release acids (specifically, acetic acid), which help reduce the pH substantially within these beds. 

So, we have biological processes occurring in botanical/leaf litter beds which a)facilitate nutrient processing in the habitat, b)contribute to the food chain, and c)potentially influence the chemical parameters of the water.

That's just like what happens in the wild habitats, isn't it?

Obviously, there is some analogous processes and benefits which occur when leaves and botanicals create a similar bed in a closed aquarium...What exactly they are is still a subject of ongoing investigation for us as aquarists. 

MICRO RANT: With so much emphasis placed on the appearance of our aquariums by some of the new vendors on the scene, it's important to remind ourselves from time to time that there are functional benefits of utilizing botanicals that go far beyond the pretty look.

We as vendors can't merely talk up the impact of "tannins" that botanicals impart from an aesthetic standpoint, and "how extreme the color" they give off, without at least sharing information about some of the important environmental impact they can have on the aquarium. We do that- and our fellow vendors shouldn't, either. Step it up, guys. We're fostering a movement here.

Now, no discussion of botanical "benefits" would be complete without the usual caveats to be responsible, prepare thoroughly, move slowly, and observe and test your water. Fishes like Apistos can be notoriously finicky and even delicate if they're subjected to rapid environmental changes.

Blackwater is not a "miracle tonic" that will make every fish thrive, but it can provide some very interesting benefits if applied with common sense. When switching over your existing, inhabited aquarium to a botanical-style blackwater aquarium with a lower ph and alkalinity, you are making significant environmental changes that can impact the health of your fishes, and the need to move slowly and carefully is mandatory. 

Okay, there's a whole lot there to unpack- drawing from a variety of scientific fields, such as biology, chemistry, and ecology, as well as from our everyday practices as aquarists. Yeah, we still don't know exactly which tannins are imparted to the water by a specific botanical. And for that matter, we don't know which tannins provide what specific effects on fishes or their aquatic environment, and what concentrations are found in their natural habitats.

And again, it's not necessarily that we are creating a new "thing"- we're simply seeing a correlation to the processes that we are fostering in our aquariums and what occurs in nature, and realizing that we can embrace, study, and benefit from them in our aquarium work.

I think that there are so many different things that we can play with- and so many nuances that we can investigate and manipulate in our aquariums to influence fish health and spawning behavior. changing botanical concentrations and such during various times of the year- creating ephemeral aquatic systems and other unique environmental-themed displays. 

I think that this could even add a new nuance to a typical biotope aquarium, such as creating an aquarium which simulates the "Preto da Eva River in Brazil in October", or whatever...with appropriate environmental conditions, such as water level, amounts of allochthonous material, etc.

Not just an aesthetic representation designed to mimic the look of the habitat- but a "functionally aesthetic" representation of a natural habitat, intended to operate like one..Full time. 

And it starts with understanding what's going on in Nature, and how we can replicate it on a more realistic level in the aquarium. Like no other time in the aquarium hobby, the information, equipment, materials, and techniques are starting to converge and create a very interesting opportunity for all sorts of hobbyists to advance the state of the art of the hobby.

Nuances. Micro-influences. Subtle steps. 

All part of "bringing up the biome", right?

Studying the influences of Nature on aquatic environments, and how to replicate and incorporate these influences into our aquariums is the key. Building a specialized aquatic microcosm in our tanks will unlock so many secrets and lead to amazing breakthroughs with our fishes- and a greater understanding of the precious natural habitats from which they come.

Stay involved. Stay excited. Stay inquisitive. Stay diligent. Stay resourceful. Stay informed...


Scott Fellman

Tannin Aquatics 




Scott Fellman
Scott Fellman


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