Do you "igapo?" Or, are you more of the "varzea" type?

It's been a long haul, but we're finally releasing those NatureBase sedimented substrates, and the response has been fantastic! We're excited, because it's the culmination of several years of dreaming, scheming, and experimenting. We're excited to see all of the cool experiments that our community will be doing with this stuff! 

Now, as we mentioned in yesterday's blog/podcast, these substrates are NOT intended to be the basic substrate for every aquarium on the planet. They are, however, ideal for "transitional" wet/dry experimental systems, paludariums, and some vivariums. And of course, the "Urban Igapo" idea that we've been talking about here for years is exactly the type of thing we intended these substrates to be used for.

I suppose that, on the surface, it's hardly an earth-shattering approach: You set up an aquarium. You don't fill it immediately. Rather, you grow some terrestrial plants and grasses, allow them to take hold...then you bring on the "rainy season" and flood it. After a few months, you begin drawing down the water significantly, ultimately returning it to its "dry" state again.

Repeat as desired.

Think about what happens in Nature in many ecosystems on a seasonal basis.

All of the botanical material-shrubs, grasses, fallen leaves, branches, seed pods, and such, which is on the forest floor- is suddenly submerged; often, currents re-distribute the leaves and seed pods and branches into little pockets and "stands", affecting the (now underwater) "topography" of the landscape.

Leaves begin to accumulate.

Soils dissolve their chemical constituents- tannins, and humic acids- into the water, enriching it. Fungi and micororganisms begin to feed on and break down the materials. Biofilms form, crustaceans multiply rapidly. Some robust varieties of grasses hang on for extended periods of time during this inundation.

Others go into a sort of "dormant" phase, "browning out" and awaiting the time when the waters will recede and once again turn the igapo into a terrestrial forest floor. 

In this rich, highly dynamic environment, the fishes are able to find new food sources; new hiding areas to spawn.

Life simply flourishes.

Each time I flood my "Urban Igapo" systems, I am utterly fascinated by how life manages to "sort it out" to not only "make it though", but to thrive. It's really cool to see the many microorganisms swimming around in the aquarium, obviously feeding among the submerged grasses and other materials.

Now, of course, I'll be the first to tell you that what you get out of this process is not what I"d ever label as a "conventional" aquarium system. Because of the high level of nutrients, dense growth of terrestrial grasses/plants, and rich terrestrial soil, it's certainly not a "recipe" for an aquascaping contest winner!

And yeah- it's not intended to be. We'll be stating this over and over again to the point where you're going to hate hearing it, I'm sure!

This is not just about cool, "Instagram-ready" aesthetics. Sure, these "Urban Igapo" systems look very cool! (And, yeah, they're pretty damn sharable on social media- I'll give you that much...). However, it's much more than that. The focus here is on studying the function and dynamics of this unique transitional environment in the aquarium.

If you're only looking for perfect, static aesthetics, you're bound to ultimately be disappointed, because- just like in Nature- the terrestrial plants will ultimately slip into a "dormant" phase, where they aren't all "crisp and green." They become stringy, limp, and brown over time. That being said, I personally find this "look" kind of cool...I think that you might, too, when this is considered in context.

I think that it's not only simply an enjoyable "hobby within a hobby"- it's a dynamic that we can can and should learn more about. When we flood and desiccate an aquarium, attempting to replicate this cycle, we have to learn to manage a number of different dynamics, ranging from varying levels of nutrients, to nitrogen cycle management, to stocking with fishes.

The seasonal dynamic is broad-reaching and multi-faceted in the aquarium, as it is in Nature.


Let's take a little closer look at how you'd make one of these systems. Now, this is the most "cursory" and basic "treatise" about how to do one of these projects. We'll have much more detailed blog, photo essays, and an instructional video that Johnny and I will produce soon. Suffice it to say, this is only the start!


First off, here's what you'd need:

-Small aquarium (5 US gallons or less)

-NatureBase "Igapo" or "Varzea" substrate 

-Grass seeds and or submersion-tolerant terrestrial plants

This is so easy that it's actually kind of embarrassing that I'm breaking down the process here, lol.

STEP 1- Add NatureBase substrate to aquarium. The depth that you will achieve is dependent upon the size of the aquarium and the amount of substrate you're using. We suggest about a 2" layer, which, if you're using one bag of NatureBase, will work in a small aquarium. Since this stuff is rather pricy, you're likely to work with smaller tanks until we really get the price down on this product with scaled-up production.


STEP 2- Add grass seeds and/or terrestrial plants.  Great plant choices are  the immersion-tolerant Acorus, and even rice seeds would be cool! Wet down the substrate as you would after any terrestrial planting. Soil should be moist but not completely saturated.


Now, a little note on grasses. We have been utilizing a few varieties of grasses, such as Paspalum and Bahia varieties. Both of these grasses are remarkably resistant to periods of submersion, and are pretty cool subjects to use in your "Urban Igapo." In fact, we're so excited about them, that we plan on offering them  soon to complement your "Urban Igapo" experiments! 

Depending upon the germination time of the seeds you're using, it's probably going to be between 7-14 days before you see some "above-the-surface action" from them, with grasses starting to sprout up!

After a few weeks of frequent watering (not too much, though!), you'll begin to see a pretty serious "lawn" growing in your little igapo!

As a side note- there is something oddly satisfying about seeing grass inside you home! For hobbyists who live in say, high-rise urban apartments, the novelty is pretty incredible, I'd imagine! 

The real fun comes next. 

STEP 3: Bring on the rain! After a few weeks/months, your little slice of the forest floor is probably doing pretty well. The grasses are thriving and your plants are no doubt growing strongly. It's time to start the rainy season! 

Slowly add water to your display until you achieve a depth pf about 1/2" (1.27cm).  When you pour, be careful and try to not disturb the substrate too much, as your grasses tend not to put down deep roots. Increase the water depth slowly, over a period of several days or longer, until you achieve he desired depth.

One of the cool things that I've noticed about the "inundation phase" in my "Urban Igapo" systems is that you start to notice organisms in the water- little aquatic crustaceans, Paramecium, rotifers, etc.- just like what happens in Nature.

This is really interesting to see! 

Now, sure , the water will be a bit cloudy at first, as the sediments and so forth leach from the substrate. However, over time, the water tends to clear up. Regardless, I generally have to used a filter in my "Urban Igapo" tanks. I find it not only unnecessary, but a bit of a distraction. You COULD use one, of course. I'd select a tiny inside power filter, sponge filter, or even just an airstone, if you're so inclined.

This is the time when you'll want to add some fish to your system! What kind of fish you want to add is up to you. I'm a fan of annual killifishes, as they're ecologically adapted to live in temporary pools, and are kind of "made" for this type of setup! However, I've done this with Tetras and other fishes as well...that's the fun part.

Do your homework and have fun!


The cool thing about annual killies is that you can keep them in one of these systems for several months, allow them to lay eggs, remove the fish, and then begin the desiccation process knowing the there are a bunch of eggs in the substrate, waiting for the next "rainy season!"

You'll find that, depending upon how long your system has been inundated, many of the grasses and most of your plants will hang on and bounce back for another round. You may want to add some more plants and/or grass seeds for the "next season", depending upon the effect you'd like.

And of course you'd keep you system in "terrestrial mode" for as long as you'd like. Since I like to keep annual killifishes in many of mine, I keep them dry for the duration of the known incubation period of the eggs. Often this is anywhere from 6 weeks to 6 moths, depending upon species.

And start the whole cycle again! And if you're lucky, some of the eggs will have made it through, and you'll have a new group of baby killies to keep the population going! Although it's not the serious breeder's choice as the most efficient way to breed killies, this approach is an incredibly rewarding way to keep these unique fish! 
The lessons to be learned and discoveries to be made by managing these systems are many. The function, process, and aesthetics are far different than conventional aquariums, yet, in an odd way, feel somehow "familiar" to us. You can do all sorts of experiments, attempting to replicate similar habitats from all over the world. 
One of my next "full size" tanks will be set up in this fashion for a few months prior to inundation. Managed initially as a "rain forest floor", and ultimately flooded (likely permanently, though). Other experiments are possible with this approach, and using botanicals and other materials in the substrate goes with the territory.

It's just the beginning of a very interesting time to experiment. A time to study, scheme, and replicate the function and form of Nature in a most unique way. And you're right in the thick of it! 

Stay creative. Stay Bold. Stay inspired. Stay excited...

And Stay Wet.

Scott Fellman
Tannin Aquatics 

Scott Fellman
Scott Fellman


2 Responses

Scott Fellman
Scott Fellman

December 15, 2020

Absolutely! I’ve done it with small characins with incredible success! The key is to not over-stock. And of course, when it’s time to begin the “dry season”, you need to remove them😆! DO IT! You’ll be totally addicted to this little “sub hobby!”


Joshua E Morgan
Joshua E Morgan

December 15, 2020

Cool! I know you mentioned annual killies, but could a recently submerged setup like this be used for fry of non-annual fishes? I imagine they would benefit from the microfauna of the newly submerged setup so long as some other problem did not interfere with the fry’s growth and survival.

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