Chasing numbers.

We talk about the idea of replicating the natural habitats of our fishes as almost a religious thing. We understand that fishes have evolved over eons to reside in specific environmental conditions and ecological niches.

And of course, sometimes, when we attempt to replicate some of these environmental conditions, they create outcomes that we might not have expected. Hoped for perhaps, but not expected.

It happened yet again...a breathless phone call from a customer who recently switched over to a botanical-style, blackwater aquarium, only to have her little Boraras, which she'd had for over a year, suddenly start spawning!


Now sure, it could just have been that they finally were of spawning age, or that the temperature in her tank changed one night, or... number of a dozen possible factors. She felt it was "something in the water" released by the botanicals that she added not too long ago (in her case, Selatan Catappa Bark and a few other items...). I can't say with any high degree of certainty that this was, indeed, the catalyst for the results she is enjoying.

However, I hear these kinds of stories from hobbyists fairly often...In fact, likely too often to think that it's merely a complete coincidence, or a set of unrelated events and random factors.

Yeah, we hear this stuff a lot.

Actually, all the time. Like, regularly.

What we're seeing more and more in botanical-stye, blackwater aquariums are reports of "spontaneous" spawnings and "pering up" of all sorts of different fishes associated with these types of conditions. 

The "common denominator" in all of the reports we receive are that the fishes are displaying better color, vigor, and overall health after being recently exposed to the more "physiologically appropriate" conditions of a blackwater aquarium. Now, this is by no means us stating that blackwater, botanical-style tanks are somehow "magical", and possess the ability to make every fish spontaneously thrive and spawn.

That's just complete B.S., and I won't ever make or support those kinds of assertions.

However, it's more of an affirmation that fishes from some specialized environments- even those which might be several generations captive-bred, can always benefit from being "repatriated" to some of the conditions under which they have evolved for eons.

But, here's the thing.

We just can't replicate every single environmental parameter of our fishes' natural habitats in our aquariums. 

We can, however, replicate many aspects of their natural habitats- chemical, ecological, and physical.  

We can.

Now, I have no illusions about what we do here. One of the things that we can do is analyze some of the ecological parameters of the natural habitats from which our fishes come, and figure out how replicate, to the best of our capabilities, the ones that we can.

This is not an "excuse" for half-assed work. Rather, it's a bit of a concession to practicality. Realistically, not everyone has the test equipment or means to manipulate water parameters so that you can get "x" mg/L of Sr, Fe, SiO2, etc. Now, I'm not saying that you can't do just may not be practical for many who don't have access to lab-grade analytical equipment and pure chemicals.


And, it's not always advisable to do so, even if you DO have the means.

We as hobbyists have for many years felt compelled to "chase numbers" in our attempts to recreate the water chemistry of our fishes natural habitats as faithfully as possible. Now, this is a pursuit which I can understand; I do have enormous respect for those hobbyists who endeavor to do this.

As a side note- I remember several hobbyists from the reef aquarium world who were scientists, and who DID try this sort of stuff, and their tanks were among the most "average" I'd seen! That being said, I did see some tanks from hobbyist/scientists who had access to incredible analytical equipment and chemicals, and they DID have amazing balances out, I suppose.

I think that the other "problem" is that we aren't exactly certain what some of these trace elements and such actually do, in terms of benefits for our fishes...We just know that they are present in the natural waters from which many of our fishes come. So, where does that leave us?

I guess I've often taken the rather sheepish response of saying that it's better to replicate some of the aspects of our fishes' natural habitats than none whatsoever. Of course, I realize that some things are important, like pH and alkalinity. Some species simply cannot spawn, have eggs develop, etc. under anything but some very tight parameters, or with the presence of specific trace elements.

Such a case came to my attention when I was visiting a killifish forum on Facebook not long ago. One of the participants was discussing some new fishes he obtained, and one was from a rare genus called Episemion. Weird, because it is a fish that falls genetically halfway between Epiplatys and Aphyosemion.

Even more interesting to me was the discussion that it's notoriously difficult to spawn, and that it is only found in a couple of places in The Congo. In fact, the type description of E. krystallinoron, one of just a handful of identified Episemion species, is described as, "...a large river (~ 5 - 6 m) up to 1 m deep. The river near Medouneu at locality G 02 / 156 (= BBS 99 / 22) is also large (~ 4 - 5 m) and about 80 cm deep. At both localities the water is fast flowing, with sandy bottom and no aquatic vegetation. Episemion specimens were found amongst overhanging terrestrial vegetation..."

Good stuff...As an aside, reading through these type papers often gives you some good info on the ecology of the ecosystems from which our fishes come from! It's really interesting stuff!

And even more interesting to me was that it is in a region known for high levels of selenium (Se) in the soil...And that's VERY interesting. Selenium is known to be nutritionally beneficial to animals and humans at a concentration of 0.05-0.10ppm. It's an essential component of many enzymes and proteins, and deficiencies are known to cause diseases. One of it's known health benefits for animals is that it plays a key role in immunity and reproductive functions!

Boom! 💥 

Okay, that helps with the "difficult to breed" part, right?

Selenium occurs in soil associated with sulfide minerals. And it's found in plants at varying concentrations which are dictated by the pH, moisture content, and other factors. As you might guess, higher concentrations of selenium are found in  in the plants which occur in these regions. 


So, I"m doubtful that we know the specific concentrations of selenium in many of the planted aquarium substrates out on the market, and most hobbyists aren't just throwing in that "readily available tropical Congo soil" - the one that you can pick up at any LFS- into their tanks, right? 😜

Oh, there isn't one...that's right.

So, how would we get more selenium into our tanks for our killies?

Botanicals could be one way.

Like, The Brazil nut...


And the Brazil nut is kind of known to us, isn't it? The "Monkey Pot" has something to do with this, right?

And, yes-  it's technically a fruit capsule, produced from the abundant tree, Lecythis pisonis, native to South America -most notably, the Amazonian region. Okay, not native to Africa, but it's possibly something we could use as an experiment to help increase Selenium in our tanks, right? Maybe? I mean, just because this fruit capsule might have traces of Selenium, does that mean that if you submerge it, some will leach out? How much? 

The "Monkey Pot/Killie" mental exercise above simply demonstrates the difficulty of actually determining what, if anything actually gets into the water from botanical materials, and if it can actually have some sort of impact. So much we don't know. And yeah, these kinds of "exercises" have lead to many assumptions- you know, like the shit I read on various vendor sites about the "nutritional value" of various leaves and such and how they can benefit shrimp because they have "such-and-such" vitamins and other compounds- which are known to do _____ in humans, therefore, they MUST impart these substances into the water for the benefit of our shrimp, right?

Urghh. Pure assumptions are rough. 

Yet, some things may be potentially verifiable with our experimentation, right?

Killifish are particularly fascinating subjects for this work, because, as we've mentioned already, they are so intimately tied to their environments, unlike so many other fishes are. And the connections between them and their environments- and the things we can learn from these relationships- are compelling and potentially game-changing in some instances.

We need to experiment.

And of course, there are those water tests.

Like any good reef aquarist, I am really into water testing. Not only because it's good to know what exactly is going on in my aquariums, but because I can compare the water quality in my tanks to that on the reefs (this information. is readily available). In my botanical-style aquariums, the water testing to me has always been to help me learn the "baselines" at which these systems operate. I mean, seeing that our more focused practice of using lots of leaves and other botanical materials in our tanks is relatively new, it's not like there is a huge database in the aquarium hobby to see what's "normal" for these types of systems.

Just like in the reef world, if you look long and hard enough, you can find all sorts of scientific papers documenting all sorts of water chemistry parameters in some of the wild habitats we obsess over. Being able to know what is "normal" for the wild habitats is a valuable asset. Of course, we can't expect to target and achieve every single parameter that we see in one of these studies of natural systems in our aquariums, However, we can use these as a sort of "point of comparison" to see what kinds of "commonalities" we can achieve between the natural habitats and our aquariums.

Of course, you can get really crazy, and just "chase numbers" to the point of actually being detrimental to your livestock. There are some parameters that you can work with that can yield interesting results. Of course, the key is not to go overboard chasing specific numbers in the process.

Redox is a great example of this.

One good aquarium source I found online defines redox (aka "ORP" or "oxidation-reduction potential") "... a measure, in millivolts, of the tendency of a chemical substance to oxidize or reduce another chemical substance."

In aquarium practice, Redox potentials are closely related to the stability of the aquarium and is often used as a 'barometer' of water quality.

Things which decrease the oxygen content of the water, such as decomposing food, fish poop, etc., can rapidly break down into more toxic compounds like ammonia and nitrite, are known as "reductive agents." These reductive agents can decrease the redox potential, which indicates deteriorating water quality. 

I remember my first measurements of redox in one of my botanical-style aquariums, I FREAKED THE FUCK OUT because I was getting a reading of 202mv, when, in the reef world, I'd been "brought up" to looking at target numbers like 350-400mv as "acceptable!"  That reading was like "sewer water" in reef tank land! 

Now, some hobbyists would use ozonizers to achieve these high redox levels, and end up essentially burning off the fins of some of their fishes in the process! It was a classic example of chasing numbers to the point of not taking into account the actual damage that we were doing to our livestock in pursuit of some target number! 

The reality is that my botanical-style/blackwater aquariums were gorgeous and simply thriving with ORP reading of around 200-240mv or so. Of course, if I were chasing what "the books" said about ORP and freshwater, I'd be trying to hit higher numbers, like 250-300mv, because...well,, why? Because "they" said so?

Yeah, I think.

I mean, thinking about numbers as absolutes is really a problem that we as hobbyists seem to get into. A real "hamster wheel" that many get stuck in. The reality, we'd do far better to fall into some sort of range for some of these parameters, and to just look at our own aquariums and see how the organisms under our care are doing.

And further, when you research the parameters of the wild habitats from which our fishes come from, some of the numbers you see reported seem to be well below what "the books" suggest that you target in the aquarium!

Again, the idea of simply chasing numbers and using that as a rationalization that you're doing everything correctly is a fool's errand, IMHO. Rather, I think it useful to study the environments and ecology of the environments from which our fishes come from, and see which ones you can replicate as accurately as possible. Or at least, which ranges, factors, or conditions you can replicate as accurately as possible.

You'll find that it's extremely difficult to replicate them exactly in most cases, because of numerous factors related to the environments surrounding the aquatic habitats we love so much. Factors like soil geology, rainfall, flood influx from surrounding streams, seasonal temperature shifts, periodic sediment and nutrient influxes, etc. are among the many variables which factor into the way these habitats evolve and function. 

One of the reasons I spent about two years of my life playing with all sorts of materials to develop the NatureBase sedimented substrates was to attempt to replicate- on some level, the influence of soil geology has on wild aquatic habitats in our closed aquariums.

The results are interesting and have been quite encouraging, but they're far from "exact." We can at least introduce some of the factors which natural soils and sediments have on aquatic habitats in our aquarium versions, and attempt to replicate some of their physical and aesthetic characteristics. I personally feel that they're more "biotopically "accurate" than most of the substrates out there, but they are certainly not the best substrates ever made.

And their very composition- silts, clays, and sediments- ensures initially cloudy conditions that would discourage all but the most hardcore hobbyists from going "all in" with them as the sole substrate in a large display tank! They're largely experimental.

Again, the joy (and frustration) of "chasing numbers", or attempting to replicate the characteristics and function of wild aquatic habitats is that it's damn hard to do it with 100% accuracy! The reality is that you can recreate a "reasonable facsimile" in many cases- which is pretty incredible, really. However, because of the enormous number of factors and influences on aquatic habitats, I personally feel that this might be as close as we can get for the foreseeable future.

Yet, I'd hardly think of that as a reason NOT to strive to try to recreate every possible parameter of Nature in our tanks. The "wins" we rack up on the way towards the impossible-to-achieve goal of 100% accuracy will only benefit our fishes and advance the state of the art of the aquarium hobby for many years to come!

So, the parting shot here is that, if you're excited like I am about the idea of replicating some of the functions and characteristics of your fave wild aquatic habitats- go for it.

However, keep one leg firmly grounded in practicality, and understand and accept that "perfection" is an unlikely outcome. Rather, it's about a process of learning, understanding, and experimentation- all done in an effort to get us closer to creating more optimum conditions for the fishes which we love so much.

Stay experimental. Stay curious. Stay bold. Stay studious. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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