After a rocky start, it's back to the bottom for us!

Well, if you've noticed lately, we're really starting to phase out rock on our website! It's pretty obvious...We've been blowing the stuff out at ahem, "rock bottom" prices lately to get rid of it! Surely you noticed, because we've never sold so much rock so quickly! Weren't aware? Well, you'd have to be "sleeping under a rock" to- okay, that's enough already!

Seriously, though, I'm finished with least, finished with selling the stuff on our site. (although we'll keep our "River Stones" and River Pebbles", 'cause I like them and they make sense!). Is this a sudden backlash against rock or something? Not really. I just don't like handling, sourcing, shipping, and selecting the stuff. It's a pain in the ass: expensive to ship, highly subjective to select, and difficult to get a good mix of sizes from our I'm done.

It also reminds me of things I hated about the coral trade...too many stupid names to keep up on, a lot of hype about any rock that some superstar 'scape uses, and a sort of lack of "romance" to me.

Oh, and the best reason?

It really isn't all that applicable to what we do.

As we delve deeper into the world of blackwater, botanical-style aquariums, I think it becomes more and more important for us to understand the wild blackwater habitats of the world. Specifically, how they form, and what their physical characteristics are. It's easy for us to just go the  "cliche' route" and say that blackwater is water, "...which has a low pH caused by dissolved organic materials and looks the color of tea."  You could just leave it at that. You know, the standard line used for decades.

Not untrue, but not really all that helpful in understanding exactly what it is, IMHO.

And more important, not helpful in understanding why it has these characteristics.

And there are some things which contribute to the overall habitat of blackwater environments- specifically, how they form.

Well,interstingly, it does sort of start with the study of rocks...Geology.

Hey, don't start yawning on me...

I should first start of by freely admitting that I sort of- well, dozed through the limited number of geology classes I took in high school and college, and never knew that the time I spent in those classes drawing pictures on the back of my notebooks and trying to figure out where to get the stuff I needed for that weekend's party would ever come back to haunt me decades later, when I'd have to re-familiarize myself with all of this stuff!

So, my understanding is limited, but I'll convey what I DO know to you here...And how it relates to our area of interest.

Blackwaters in areas like Amazonia (one of our fave locales, of course!) drain from an area known to geologists as the "Precambrian Guiana Shield", which is comprised of sediments include quartz, sandstone, shales, and conglomerates, stemming from the formation of the earth some 4.6 billion years ago. As a result of lots of geological activity over the eons, a soil type, consisting of whitish sands called podzol is formed.

Podzols typically derive from quartz-rich sands, sandstone, and other sedimentary materials in areas of high precipitation. (Hmm, like The Amazon!). Typically, Podzols are kind of shitty  for growing stuff, because they are sandy, have little moisture, and even less nutrients!  

A process called podzolization (of course, right? What the fuck else would you call it?) occurs where decomposition of organic matter is inhibited. Numerous microbes and plants consume some of the nitrogen, and while eaten by other organisms, convey what's left to the even lower-lying forest habitats.

The Amazonian blackwater rivers are largely depleted in nutrients, having passed through the lowland forest soils as groundwater, from which weathering has already occurred. As a result, layers of acidic organics build up. With these rather acidic conditions, a deficiency of nutrients further slows down the decomposition of organics. So, yeah- lousy soil for growing stuff...But guess, what? They form the basis of the substrate in many Amazonian aquatic habitats! 

And the water which flows over this soil is what we call "blackwater",  which achieves it's unique color from a really high content of dissolved  humic substances- poor in nutrients and electrolytes. It's characterized by having sodium as one of its major cations (ions with fewer electrons than protons, giving them a positive charge), which means it has low alkalinity. Typically, the pH and electrical conductivity values are less than 5.0 and 25 μS cm–1, respectively (pretty freakin' low!).

So, to make a very long and intimidating story short, the physical characteristics of blackwater habitats are influenced as much by the geology as anything else!  

That is to say, all of the dissolved humic substances which give these bodies of water their unique look are "enabled" by the geological properties of the region. And from the "trace element perspective" (the reefer in me), only Fe, B, Sr, Pb and Se present consistent concentration variabilities sufficient to influence the chemistry of these waters...Like, this water has very low concentrations of trace elements.

That's why you'll often see simple fine, white silica-type sands on the bottoms of so many Amazonian streams and rivers. They originate up in the Andes mountains and are transported by various means into the lowland areas. I mean, there is way more to this process than I can convey here- but it's a study in the relationship between seemingly unrelated elements and how they come together.

Now, I admit that this is probably more than you will ever care to know about how sand works in your fave blackwater habitats, but I think it's important to understand that it's all kind of related. In fact, it makes it a lot easier to understand how blackwater systems came to exist and function when you consider this "big picture" stuff!

And of course, we're a hell of a lot more interested in the "decaying vegetation" (you know, the leaves, twigs, seed pods...stuff like that!) which influences the waters.

So, using a quality substrate material which doesn't impact the pH or buffering capacity of the water to any great extent is important...The reality is that just having an awareness of what goes on in the natural aquatic habitats we love gives us a nice "leg up" on this stuff. You're obviously not going to use a strongly buffering substrate like aragonite or whatever to do the job in your low pH and alkalinity blackwater aquarium, right?

And then there is that question about utilizing rocks in your "igapo" aquascape...

Like, why don't you find rocks in these habitats? 

As you know from my long-winded description above, I'm no expert-or even a novice- on geology or geochemistry, or anything in that subject area, for that matter....However, based on my research into this stuff, as related above, it goes without saying that these are hardly conditions under which rocks as we know them could form.

Oh, sure, you might find the random rock in the igapo that was washed down from the Andes or some other high-country locale in these forests, but it's a pretty safe bet that it did not evolve there. This also helps to explain why the blackwater habitats are generally low in inorganic nutrients and minerals, right? 

So...if you're really, really hardcore into replicating an igapo, you'd probably want to exclude rocks- especially if you're entering one of those biotope aquarium contests, astute judges would (rightfully) nail you on scoring for falling back on your natural inclinations as an aquascaper and tossing some in. 

I personally, of course, would be a bit more forgiving, but you won't find rocks in my igapo tanks!

Besides, there is something far more compelling and romantic about leaves, seed pods, and wood than there is about a bunch of rock, right?


Okay, don't answer that...

Yeah- you WON'T find any rocks in my "igapo" tanks...


I just can't say that I]m really into them.

Rather, we choose to concentrate on the more "ephemeral" components of the habitat, and rightfully so!

Our ability to mimic this aspect of the flooded forest habitats is a real source of benefits for the fishes that we keep- and a key to unlocking the secrets to long-term maintenance and husbandry of botanically-influenced aquariums.

The transformation of dry forest floors into aquatic habitats provides a tremendous amount if inspiration AND biological diversity and activity for both the natural environment and our aquariums.

Flood pulses in these habitats easily enable large-scale "transfers" of nutrients and food items between the terrestrial and aquatic environment. This is of huge importance to the ecosystem. As we've touched on before, aquatic food webs in the Amazon area (and in other tropical ecosystems) are very strongly influenced by the input of terrestrial materials, and this is really an important point for those of us interested in creating more natural aquatic displays and microcosms for the fishes we wish to keep.

Creating an aquascape utilizing a matrix of leaves, roots, and other materials, is one of my favorite aesthetic interpretations of this habitat...and it happens to be supremely functional as an aquarium, as well! I think it's a "prototype" for many of us to follow, merging looks and function together adeptly and beautifully.

Way sexier snd more interesting to me than any "Iwagumi" layout everyone drools about...Far more compelling than some "new" rock with a stupid name that people get all emotional about.

I like roots, twigs, seed pods, leaves, wood, and soils

Now, I think at least part of the reason why we're seeing success with utilizing botanicals in our aquariums is that fishes are instinctively "programmed" to utilize many of these materials as both feeding substrates- and as food items in and of themselves. (Yeah, "pellets and flakes" are NOT part of their natural diet... 😆)


Oh, but what about rocks in blackwater tanks? "Stay on topic, Fellman!"

Well, yeah, you CAN play with rocks in a blackwater aquarium. Nature has a prototype for THAT... You just need to study a bit.

In fact, you can have, rocks, leaves, wood and blackwater all together. It's just about context. It's about understanding how and why these materials come together, what factors conspire to cause this, and what can happen when it does.

Yeah, you can do it. You just won't be able to get many rocks from us! What are we going to replace our rock selection with? Something near and dear to my heart:

Substrate materials.

We've been busy formulating and testing some unusual substrates and creating variations that have not previously been offered in the trade before. Stuff that is perfectly suited for what us botanical-style, blackwater and brackish aquarium geeks do. Stuff that is designed to replicate, in form and function, the materials found in the natural habitats of our fishes.

So, for a lot of reasons, I think rocks are probably the least applicable materials we can offer...of course, the facts can go either way.

That being said...

A little research into these seemingly obscure, and perhaps unrelated topics can sometimes give us some awesome clues that can influence our aquarium practice in ways we haven't even imagined. Clues which may lead to further evolutions and improvements to our practices. Clues that can help us continue to create compelling aquatic displays.

So, when you see me unloading rocks at stupid low prices, you'll at least have a little bit of context, right?

I hope so!

Stay engaged. Stay intrigued. Stay curious. Stay diligent. Stay informed. Stay inspired...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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