Flooding your own rain forest..Simulating an igapo in your aquarium?

We've seen more and more really cool experiments with leaves and botanicals in aquariums, and I correspond with hobbyists daily who are interested in incorporating leaf  litter beds- or rather, simulating leaf litter bed biotopes in their aquariums. With all of the interest in keeping aquariums filled with leaves, it's a good time to talk about the wild leaf beds for a little more inspiration, and to help you with your "scheming!"

Some of the more dynamic leaf-litter zones in the Amazon region (my sort of "go-to" biotope for inspiration) are annual features, found in rain forests on low-lying tributaries of major rivers. Under the influence of these larger rivers, you will see various water depths based on the annual cycle of inundation. This influx of water floods surrounding rain forest areas, and the result is a feature called an igapo.

Obviously, a flooded forest floor has a lot of leaves and botanical materials accumulated, which influences the "topography" and water chemistry of this habitat. Often, these areas form channels a few meters wide, and result in "meanders", which are pockets of water that course away from- and back to- the main streams. During the low water season, you'll see the leaf litter accumulating in these "meanders", with the diversity of life they contain.

Although igapó forests are characterized by sandy acidic soils that have a low nutrient content, the tributaries that feed them are often found over a fine-grained, whitish sand, so as an aquarist, you a a lot of options for substrate!

How deep are these litter  beds? Well, they can range from just a few inches deep to a few foot or more, depending upon the prevailing water movement, topography, and time of year. Interestingly, the fishes that inhabit these beds and the areas adjacent to them tend to stay in their little "niches", so for the aquarist planning such a system, you can created a community of fishes that each have their own "territory", if you will- a really cool idea to consider when stocking a tank!

First off, from a purely "compositional" standpoint, the leaf litter bed in an aquarium can and should consist of whatever leaves you enjoy. Obviously, we are big fans of tropical leaves, such as the much-loved Catappa leaf, as well as Guava. More recently, we've embraced some new leaves, such as Jackfruit, Loquat, and Magnolia- leaves from entirely different parts of the world, which lend a different look, aesthetic, and "functionality", if you will- to an aquarium leaf litter bed.

It's important to incorporate botanicals with long "functional life spans" when contemplating a deep leaf litter bed, because replacing these materials often could become a chore! Of course, that's why we now offer larger packs of leaves- to keep your life simple!

As we've discussed before, Amazonian leaf litter beds are home to a surprising variety and population density of fishes, with some studies of igapos yielding as many as 20-40 different species of fishes in a 200 square meter area!  And, the majority of the specimens found in these studies are small, averaging around 40mm-100mm (1.5"- 3.9") in length! This is interesting from an aquarist's perspective, because we can create a pretty dynamic and interesting environment, with lots of cool small fishes,  if considerations are made for tank size, filtration and husbandry. 

I would encourage you to utilize several different types of leaves in your litter bed, for the simple reason that each type has different "durability characteristics." I always make it a point to include the more transient Catppa, with a larger "base" being durable leaves, such as Magnolia, and a slightly smaller percentage of Guava. This way, you've got leaves in various stages of decomposition in your system at any given time, lending a cool look and imparting a more consistent "tint" to your water.

Of late, I've played more with just leaving my leaves alone for longer periods of time, with less new leaves going in, and leaving the decomposing leaves in until they're gone. This has created a very stable appearance, nitrate and phosphate reading, and pH. Not that these were issues before when I was constantly exchanging leaves, but I do notice a much more consistent pH in the tank. Nitrate and phosphate have rarely been above minimally detectible levels. However, being a sort of biological "yardstick" for water quality, it's nice to keep them as low as possible. (the reefer in me talking here...).

Who's going to try a display with a really deep (like 5-8 inches) leaf litter bed? Can it be done? I don't see why not, if provision is made for aeration, filtration, and water quality management.  You just need to understand what's going on in the tank, and to find its "normal operating values" in terms of pH and other water quality parameters. I would think that this would be a situation when it would be advisable to steep many of the leaves for much longer periods of time before use, to leach out a lot of the initial tannin they contain, so their impact on the pH of the water is moderated just a bit.

As we've discussed before, maintaining a very acid tank (like below 6) presents a set of challenges that will keep you on your toes. In particular, the biological filtration provided by beneficial bacteria, which we take for granted in most aquariums, essentially shuts down at really low pH values, which would leave you dependent upon zeolites and/or other chemical filtration media for successful operation.  I would do some studies on the pH over a few days or even a longer period before adding fishes, to get a feel for how such a leaf-heavy system performs. You could employ a buffering sand substrate to moderate this pH somewhat...again, much room for responsible experimentation here!

Piqued your interest yet? Perhaps you'd be breaking some new ground, aquarium-wise, in terms of trying something a bit different!

At the very least, I may have given myself the motivation I need to push forward and create an agape biotope in my own home!

Until next time...

Stay daring. Stay innovative. Stay excited...

And Stay Wet.

Scott Fellman

Tannin Aquatics



Scott Fellman
Scott Fellman


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