The allure of water...

As fish geeks, we spend an absurd amount of time pouring over online catalogs of filters, plants, driftwood, and other gear. Each year, it's safe to guess that we collectively spend tens of millions of dollars on all of this stuff. Yet, one of the items on the "aquarium checklist" that seemingly receives so little attention or consideration from many is...water.

Yeah, the water. 

Now, sure, some hobbyist rightfully place the importance of good quality, properly-conditioned water at the very top of their "want list" of "Stuff" required for successful aquariums. These are often fish breeders and very serious hobbyists, who understand the fundamental importance of good water.

So, yeah- it goes without saying that the single most important component of our aquariums is also the most obvious...water! As the literal bearer of life and the environment in which our fishes, plants, and other organisms thrive, it's fundamental. it's the reason we're drawn to fishes, not gerbils, Tarantula, or Mice- or whatever other pets people keep!

Yeah, we're into water!

And I dear say that we take it for granted a bit.

Have you ever thought of how water actually gets into those bodies of water (streams, rivers, etc.) that we find so compelling?

Well, sure, the first two things that come to mind are precipitation and runoff from the higher mountains. And that's perfectly logical and correct. However, if you consider some of the other  processes by which water makes it into our favored habitats, it's actually quite interesting, and maybe even has implications for the way we prepare water for our aquariums.


Sure, some simply falls into the body of water directly from the sky, and that's that. Some is a result of overflowing streams and rivers (like, ya' know- those flooded Igapo forests we talk about!). Inputs of precipitation falling over the area of an aquatic habitat are transferred to the habitat via a number of different pathways.

It's surprisingly complicated.

There's like a whole field of science devoted to studying this process! 

However, not all of the water has such an easy journey on its way into our favorite aquatic habitat!

Even in the case of rainwater, some of it simply lands on tree leaves in the surrounding area and evaporates. This is a process scientists call "interception", and accounts for the fact that not all water makes it to the ground. Water that does reach the ground enters the soil through a process called infiltration. slowly percolating down to soil areas known as the "saturated zone"- and as you'd imagine, this is where the fun really begins! (to a soil geologist, at least!)

The soil properties control the infiltration capacity; these include things like soil permeability, the presence of vegetation and plant roots, and how much water is already in the soil. Through what is known as "ground water flow", ultimately, the water finds it way into our favorite aquatic habitats. Soil texture ( the relative proportion of sand, silt and clay particles within the mix) affects infiltration rates. 

Sandy soils like the "podzols" that we've talked about have higher permeability than some clay soils. In some really arid areas a "crust" can form on the soil surface, decreasing the permeability. And of course, the thickness of the soil directly affects how much water the soil can actually absorb.

During that journey into the (aquatic) habitats, materials like humic substances, minerals, etc. will be absorbed into the water from the surrounding soil. Yeah...that's the interesting part: The surrounding geography and geology have as much to do with the ultimate water characteristics as anything else! Like so many things in nature, everything is somehow interrelated!

Once again, bringing it all back to a more practical aquarium point of view, I can't help but wonder if working with different types of substrate materials (soils, sands, etc.) in our "makeup water containers could yield some similar effects to those we see when we steep leaves and botanicals in the water. Could the right combination of soils in both our makeup water containers and even in the aquarium create even more realistic water conditions for our fishes and aquatic plants?

One can only wonder...

It makes a ton of sense.

We're seeing more and more specialized "aquatic soils" for plants which are designed to simulate some of the natural habitats in which they are found. Well, fishes are typically found in those habitats, too, right?

Why should the plants have all the fun?

Wouldn't it make sense to utilize some of these specialty substrates, or substrates comprised of some of these components in tanks which feature fishes and not just plants (or even devoid of plants?). What potential benefits for our fishes could be gained by using these more "technical" aquatic plant substrates in our fish-centric botanical-style blackwater aquariums? 

With water finding its way into the streams, rivers and other areas from so many sources, there is probably so much we can learn from finding out more about the surrounding areas  themselves, and how water ultimately makes it into the bodies of water we are so obsessed with. This is an area of study in the hobby that's really wide open for advancement, IMHO. The possibilities are endless here!

In a blackwater environment, the color is a visual indicator of an influx of dissolved materials that contribute to the "richness" of the environment. Indeed, a blackwater environment is typically described as an aquatic system in which vegetation decays, creating  tannins that leach into the water, making a transparent, acidic water that is darkly stained, resembling tea.

Despite the appearance, as a general rule, blackwater rivers are lower in nutrients than clear rivers. They have very low concentrations of major ions, such as sodium, magnesium, potassium, and calcium, and lower conductivity and typically low levels of dissolved solids. Wouldn't it be interesting, when contemplating more natural biotope/biotype aquariums, to study and take into consideration the surrounding geology and physical characteristics of the habitat?  

As we know now, the influence of factors like soil, and the presence of terrestrial materials like seed pods, leaves, and branches play a huge role in the chemical composition and appearance-of the water. It's really no different in the aquarium, right? Tannins from wood and botanical materials will leach into the water, providing the characteristic "tint" that we've become so accustomed to in our little niche.

Studying the characteristics of the igapo and varzea forests of Amazonia is just a start...these are the "textbook" examples of geologic influence on the aquatic environment- something that we can really run with in our biopic interpretations of this habitat.

Yes, I also have this irresistible curiosity about the potential of botanical-influenced substrates to foster denitrification. With the diverse assemblage of microorganisms and a continuous food source of decomposing botanicals "in house", I can't help but think that such "living substrates" create a surprisingly diverse and utilitarian biological support system for our aquariums.

I think that the idea of an "enriched substrate" will become an integral part of the overall ecosystems that we create. Considering the substrate as both an aesthetic AND functional component- even in "non-planted" aquariums, opens up a whole new area of aquarium "exploration."

And it's impact on water is already an obsession to many of us, right?

I envision that the future of mainstream aquarium practice may include creating such a substrate as simply part of "what we do." Adding a mix of botanical materials, live bacterial and small organism cultures, and even some "detritus" from healthy aquatic systems may become how we establish systems.

It's not some amazing "revolution"- it's simply an evolution of practices that we've been playing with peripherally for decades in the hobby. It's a way of looking at what's already working and trying to figure out the "whys" as we go. 

And the interactions of these materials with water and the overall aquatic environment in our tanks AND in Nature, have enormous implications for the future of our hobby. 

Water is a sort of "blank canvas"- a starting point...a "media" for our work. So many possibilities...


THAT'S the allure of water!


Stay intrigued. Stay curious. Stay innovative. Stay engaged. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 





Scott Fellman
Scott Fellman


2 Responses

Scott Fellman
Scott Fellman

July 27, 2019

Hi Luke!

Happy this one touched you. I think that we are at a truly exciting point in the hobby..a time when we can look at Nature in an unbiased, “unfiltered” way and make the mental jump to understand how and why it looks and functions as it does, and how these things impact our aquariums…how we can work WITH them, instead of trying to “sanitize” them for our use. And by understanding the relationship between the soils and terrestrial habitats and the aquatic ones, we can unlock a lot of interesting stuff! Let’s get after this! :)


Luke Casteel
Luke Casteel

July 27, 2019

This has to be the most intriguing and gripping articles that ive read in a long time.
I am extremely interested in this – its no doubt i will go on with my day, all the while wondering about a river habitat directly influenced by the surrounding lands/soils.
Thank you for giving me somthing to be truly fascinated over…

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