Filling in some 'blank spaces" in the blackwater aquarium game...


"Don't go chasing waterfalls. Please stick to the rivers and the lakes that you're used to..." -from "Waterfalls" by TLC

Okay, I have no idea why the hook from a throwaway 1990's hip-hop song enters my head every time I contemplate writing something that displays my meager understanding of science, but this is where we are at today...I felt it oddly appropriate, actually.

So, I've had this idea for a while...

And a very brief conversation the other day with James Sheen of BlackwaterUK brought this to the forefront of my mind yet again, so I'll blame him for inspiring me to make this blatant display of my ignorance possible! :)

And, on a Monday, no less...I place my head on the proverbial chopping block in the interest of spurring more discussion and research on a topic that I think needs it!

Hello, scientists....

We talk a lot about creating and extremely rich, biodiverse habitat for our fishes, using various substrate mixes, wood, and combinations of leaf litter and aquatic botanicals. Now, we've reviewed extensively the impacts, good and bad- of building up such litter beds in our existing aquariums in this column. We've oft-repeated our plea to go slowly and judge the impact of the additions of the new materials on the water chemistry and other parameters of the aquarium and it's inhabitants. 

What we haven't discussed much is the potential utility and impact of starting a new system with  a significant amount of botanical materials from "day zero." I mean, with a lot of decomposing material which essentially function as bioload in the system, would this create a more rapid or prolonged initial break-in period? Would the tank cycle more quickly, slower, or not at all? 

It's something that we discussed briefly before, and it's kind of interesting, really. Especially in the lower pH arena in which we tend to play. I think that the occasional bad outcomes we have are a result of misunderstanding or miscalculating the effects of identification and such in our lower pH, botanical-style blackwater aquariums.

I think it starts with pushing it too hard when it comes to denitrification.

In lower pH systems, an entirely different class of organisms, known as Archea, perform the role of denitrification more traditionally associated with Nitrosomanas and NitrobacterArchaeans include inhabitants of some of the most extreme environments on the planet. Some live near  vents in the deep ocean at temperatures well over 100 degrees Centigrade! Others reside in hot springs, or in extremely alkaline or acid waters. They have even been found thriving inside the digestive tracts of cows, termites, and marine life where they produce methane (no comment here)  They live in the anoxic muds of marshes (ohhh!!), and even thrive in petroleum deposits deep underground.

Yeah, these are pretty crazy-adaptable organisms...The old sayings that "If these were six feet tall, they'd be ruling the world..." sort of comes to mind, huh?

With their incredible adaptive nature, Archea can cycle a low-pH aquarium, and reach significant population densities once they get going. The whole idea is for them to have sufficient time to build up a population which can tackle the ammonia produced by the bioload of the aquarium. And ammonia, the nastiest byproduct of the cycle, can be in two forms. Toxic (to the fish) ammonia ( NH3)  occurs when the ph is greater than 7.0.  Ammonia occurs as "non-toxic" (okay, maybe "less toxic" is a more responsible descriptor?) ammonium when the ph is below 7.0. And we certainly have to consider the impact of ammonia on our systems, right?


With the traditional nitrification cycle, there are a couple of important requirements: An anoxic environment-  It is only when the dissolved oxygen is depleted that denitrifiers begin using nitrate for respiration, which begins the denitrification reaction. The other requirement is for a sufficient amount of organic carbon to be present, and this is typically found in abundance in a new aquarium filled with stuff like botanicals, etc.

What a lot of aquarists who run very low pH systems report is that the "cycling process" takes longer to complete. This definitely correlates with my personal findings, although I've personally never managed a system with a pH much below 5.5 pH; this is where the "outer limits" of low pH aquariums starts for most, and this is the realm of Archaea, as the Nitrosomanas and Nitrobacter barely function at that point. And once again, the key ingredient to managing a low pH system (like any system) is our old friend, patience! It takes longer.

At very low (aquarium-context here) pH, water quality management is essential. This consists largely of water changes, use of chemical filtration media as required, and very slow additions of animals- and botanicals- to the system. Things like biological oxygen demand (BOD) and the ability of a biological filtration system to tackle increases in bioload are far more critical at these lower pH levels. Small, consistent moves are important.

So, this admittedly spotty look at the nitrogen cycle sort of takes us full-circle back to my thoughts about a brand new tank and botanicals. I'm thinking that if you're the the who wants to go with a large amount of botanical materials (leaves, pods, etc.) from the start- from "day zero"- that you should do this without any preconceived notion about adding fishes for a while. I'm thinking that a true "fishes cycle" IS possible with a heavily-laden botanical aquarium, as these materials most definitely constitute a "carbon source!" And I suppose that "hyper-loading" all of this stuff (if you're doing it that way) in a fishless tank from "day zero" is the responsible way to go about it.

Of course, I base this purely on "experiments" I've done with tanks set up in this fashion, and with the positive results I've seen by being patient. Oh, and a fair amount of good-old speculation. See, I told you I'm opening myself up for mass criticism from scientifically-minded hobbyists today. Well, someone has to at least get the discussion started, right? I have no properly-constructed experiment done, with controls and such, to prove anything beyond the shadow of a doubt, so it's all theoretical at this point. However, I think that, for those who are not afraid of this kind of stuff, some properly constructed experiments could prove very beneficial!

I suppose, however, for most of us, we'd start a new tank or an existing one with a reasonable amount of botanicals and gradually add/replace as necessary. This certainly gives the bacterial populations more time to adjust to the increase in bioload, and for the dissolved oxygen levels to stabilize in response to the addition of the materials added-especially in an existing aquarium. Going slowly when adding are botanicals to ANY aquarium is always the right move, IMHO.

"OMG, Fellman! Patience. We get it!"

And for those of you who are fascinated by the naturally-occurring low pH blackwater systems of the Amazon, like me, I leave you with this interesting tidbit from one of my favorite scholars on these natural habitats, Peter Alan Henderson, from a survey he conducted of a leaf litter system in an Amazonian blackwater stream:

The stream was of the typical blackwater type with a pH between 2.8 and 3.5, the lower figure being lower than any previously recorded for this water type. Leenheer (1980) attributes 85% of this acidity to organic acids and the rest to CO2. Given the low level of inorganic ions in solution the acidity must certainly be due to organic compounds. However, humic acids which are fre- quently assumed to be the major constituent are not strong enough acids to produce such a low pH. A possibility is that fermentation within the litter banks is releasing strong organic acids such as acetic acid. In temperate regions acid waters are associated with reduced faunal diversity and fishlessness (e.g. Beamish & Harvey 1972), but we recorded over 20 species of fish, showing that naturally acidified systems can support diverse fish faunas. The exceptional acid tolerance of Amazonian fish has been discussed by Dunson et al. (1977).

That's a lot to digest, but very, very interesting, right? Now the pH level in this stream is well below anything a sane aquarist would attempt to recreate in his/her tank, yet the implications and ideas expressed in the passage are tantalizing, aren't they? Fermentation! Woah. Further, he speculates that "...given the pH of the water, it is likely that fungi and not bacteria are the dominant decomposers..."

So, yeah- we really are breaking new ground in our blackwater/botanical-style aquarium "practice", aren't we? Some of us push it really hard, and are dancing on a razor's edge between success and disaster. Others are more conservative, and still other aquarists playing in this realm fall somewhere in between. With so many real unknowns, and very little in the way of solid, aquarium-derived experimentation and information on the serious management of lower pH blackwater, botanical-driven systems, everyone's experiences- good and bad- are very important to the art and science of aquarium keeping. 

I've said it before and I'll say it again: This stuff isn't for everyone. The aesthetics and functions of these types of systems require real mindset shifts, careful observation, and control of our typical "aquarist compulsions" in order to be successful! Yes, patience. And yes, there is plenty of room for stuff to go wrong if we push too hard. Just like in the early days of reef keeping, or even the "high tech" planted tank specialty- we simply need to keep moving forward and experimenting; going with our "gut" in some areas, or relying on specific data in others. There will be heartbreaking failures with favorite fishes being lost. There will be spectacular successes and incremental knowledge "wins" along the way, too. This is the reality of "ground floor" operations in the aquarium world. High risk. High reward.

It's exciting. It's scary. And yes, it IS incredibly rewarding.

Glad ot have you along for the ride as we fill in a LOT of "blank spaces" in the body of work that is the blackwater, botanical-style aquarium game.

Stay brave. Stay curious. Stay patient. Stay observant. Stay undeterred.

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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