"Indoor field work..."

Have you ever noticed how what is "normal" practice to us is a bit- well, "unconventional"- even "crazy" to others in the hobby?


When I describe our little hobby niche to other hobbyists who have different areas of interest, it's interesting that I'm usually met with looks of disbelief, and the occasional inquiry as to why we do what we do with our aquariums.

I totally get it, too.

I mean, to the hobbyist unfamiliar with our little niche, it does seem a bit odd that we take a "perfectly clean" aquarium and throw in a large amount of leaves and seed pods and stuff to...decompose on the bottom! This sort of goes against the grain of mainstream aquarium thinking!

We do add a lot of biological material to our tanks in the form of leaves and botanicals- and this is perfectly analogous to the process of allochonous inputmaterial imported into an ecosystem from outside of it. Yeah, it's exactly what happens in the flooded forests, meadows, tropical streams, and rivers that some of us obsess over!

There's been a fair amount of research and speculation by both scientists and hobbyists about the processes which occur when terrestrial materials like leaves and botanical items enter aquatic environments, and most of it is based upon field observations.

As hobbyists, we have a rather unique opportunity to observe firsthand the impact and affects of this material in our own aquariums! I love this aspect of our "practice", as it creates really interesting possibilities to embrace and create more naturally-functioning systems, while possibly even "validating" the field work done by scientists!

It goes without saying that there are implications for both the biology and chemistry of the aquatic habitats when leaves and other botanical materials enter them. Many of these are things that we as hobbyists also observe every day in our aquariums! We see firsthand how leaves and botanical materials impact the life of our fishes and other aquatic organisms in these closed systems.

"Indoor fieldwork", if you will!

That's what we do...

Phenomenon such as the appearance of biofilms- long a topic that simply never came up in the hobby outside of dedicated shrimp keepers- are now simply "part of the equation" in a properly-established botanical-style aquarium. We understand that they appear as a normal part of the process when terrestrial materials become submerged under water. We're seeing them for the benefits they provide for our systems, rather than freaking out and panicking at their first appearance!

This is a fairly profound shift in the hobby, if you ask me!

A lab study I came upon found out that, when leaves are saturated in water, biofilm is at its peak when other nutrients (i.e.; nitrate, phosphate, etc.) tested at their lowest limits. This is interesting to me, because it seems that, in our botanical-style, blackwater aquariums, biofilms tend to occur early on, when one would assume that these compounds are at their highest concentrations, right? And biofilms are essentially the byproduct of bacterial colonization, meaning that there must be a lot of "food" for the bacteria at some point if there is a lot of biofilm, right?

More questions...

Does this imply that the biofilms arrive on the scene and peak out really quickly; an indication that there is actually less nutrient in the water? Is the nutrient bound up in the biofilms themselves? And when our fishes and other animals consume them, does this provide a significant source of sustenance for them?


Oh, and here is another interesting observation:

When leaves fall into streams, field studies have shown that their nitrogen content typically will increase. Why is this important? Scientists see this as evidence of microbial colonization, which is correlated by a measured increase in oxygen consumption. This is interesting to me, because the rare "disasters" that we see in our tanks (when we do see them, of course, which fortunately isn't very often at all)- are usually caused by the hobbyist adding a really large quantity of leaves at once, resulting in the fishes gasping at the surface- a sign of...oxygen depletion?

Makes sense, right? 

As I've said repeatedly, if we don't make the effort to try to understand the "how's and why's" of Nature, and attempt to skirt Her processes- she can and will kick our asses! 

These are interesting clues about the process of decomposition of leaves when they enter into our aquatic ecosystems. They have implications for our use of botanicals and the way we manage our aquariums. I think that the simple fact that pH and oxygen tend to go down quickly when leaves are  initially submerged in pure water during lab tests gives us an idea as to what to expect.

And a sort of "set of expectations" is always nice to have when you're pursuing unusual approaches in aquarium jeeping, right?

A lot of the initial environmental changes in our aquariums will happen rather rapidly, and then stabilize over time. Which of course, leads me to conclude that the development of sufficient populations of organisms to process the incoming botanical load is a critical part of the establishment of our botanical-style aquariums.

Here's another thing to consider: Inputs of terrestrial materials like leaf litter and seed pods can leach dissolved organic carbon, rich in lignin and cellulose.  Factors like light, mineral hardness, and the bacterial community affect the degree to which this material is broken down into its constituent parts in this environment. Or, if the resulting breakdown creates some "algae fuel"- right?

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

Lignin is a major component of the stuff that's leached into our aquatic environments, along with that other big "player"- tannin. What benefits does lignin provide in the aquarium context? I mean, does it provide any benefits?

Of course, we're sort of into tannins, right?

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!

Holy @#$%!

And of course, tannins in leaves, wood, and plant materials tend to be highly water soluble, helping to create 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).

And it just goes to show you that some of the things we could do in our aquariums (such as utilizing alternative substrate materials, botanicals, and perhaps even submersion-tolerant terrestrial plants) are strongly reminiscent of what happens in the wild. Sure, we typically don't maintain completely "open" systems, but I wonder just how much of the ecology of these fascinating habitats we can replicate in our tanks-and what potential benefits may be realized?

Yes, 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 would be a huge advantage for us.

The real message here is to not be afraid about learning about seemingly complex chemical and biological nuances of blackwater systems. At least, on the level that we need to have a basic understanding of what to expect in our aquariums. Nature offers many clues, nuances, and ideas for us to run with.

As our practices evolve, I think that it's important to take a more "holistic" approach. One that takes into account the ionic content of the source water, the careful addition of substrate, botanical materials, wood, and the other aspects of our unique aquariums which will make them some of the most realistic representations of Nature yet attempted.

Observation, experimentation, and iteration are all important parts of the puzzle here.

Time for more "indoor field work."

Who's in?

Until next time,

Stay resourceful. Stay curious. Stay motivated. Stay creative. Stay thoughtful. Stay excited...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


2 Responses

Scott Fellman
Scott Fellman

November 04, 2019

Hey Joshua,

That’s an interesting bit of info! And I think it makes sense, right? They come from an environment filled with this stuff, so it is likely that the materials foster such biofilms, fungal, and microbial growths..I love the idea of a “botanical-style nursery” for these fishes! Food production/sequestering is just one of the many likely benefits/fucntiosn of these materials in their natural habitat…and in the aquarium, perhaps?


Joshua E Morgan
Joshua E Morgan

November 02, 2019

Most intriguing! I have read that Boraras sp. fry are very difficult to rear if they are not provided with leaves or driftwood in the rearing tank…doubtless they are adapted to feed on the resulting biofilms as a first food, as other suitably sized foods are scarce in their native blackwater habitats.

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