Approaches, observations, management...and algae!

We focus a whole lot about the practices involved in setting up botanical-style aquariums, the nuances in their evolution, and the "best practices" involved in managing them. However one of the things that we're overdue for another discussion on is the long term expectations of what happens in such a system.

Specifically, what happens in an aquarium where we have this enormous amount of botanical materials breaking down?

First off, let's clarify some stuff. Despite the seemingly laissez-faire style of "a whole lotta stuff" accumulating in the aquarium, it's not just, "Drop in leaves and forget." There is a fair amount of technique there. Technique, married with long-utilized common-sense aquarium husbandry practices.

I am a big believer in stability, and deploying patience, using time-honored nutrient control/export techniques, and applying a healthy dose of observation and common sense all contribute to the ultimate stability and success of our blackwater/botanical-style aquariums- just as they would to any other type of system.

One of the things that we all experience with these types of systems is an initial burst of tint-producing tannins, which likely will provide a significant amount of "visible tint" to the water. If you're not using activated carbon or some other filtration media, tis tint will be more pronounced and likely last longer than if you're actively removing it with these materials!

You might also experience a bit of initial cloudiness...this could either be physical dust or other materials released from the tissues botanicals, or even a burst of bacteria/microorganisms. Not really sure why, but it usually passes quickly with minimal, if any intervention on your part. Oh, and not everyone experiences this...often this is a phenomenon which seems to happen in brand new it might not even be directly attributable to the presence of the botanicals (well, at least not 100%). Could be the sand, or other dust/dirt from the other hardscape materials or the tank itself.

And of course, as we've discussed, it's perfectly normal for the water in botanical-style aquariums to have a little bit of "texture" to it- a sort of normal by-product of the breakdown of the materials we use.

While we're on the subject of new tanks, one of the things I've noticed about my botanical-style/blackwater aquariums is that they "cycle" very quickly. Like, often in less than a week. Why? I think it's got something to do with a large influx of botanical materials in a new system. The same factors that would endanger an established system might simply contribute to a rapid growth of bacteria.

Interestingly, over the years, I've also found that nitrate accumulation tends to be almost nonexistent in my botanical-style aquairums. Now, I don't know if that's something which you've noticed, too? I simply have never seen a nitrate accumulation more than 0.2mg/L!

Despite what I hypothesized would happen in my early years of playing with this style of aquarium, when I really got into blackwater, botanical-style aquariums, I found that they almost always produce little to no detectible nitrate, despite utilizing a lot of botanical material within the tank that was breaking down. I would have thought, at least on the surface, that there would be some detectible elevated nitrate. Now, this is interesting, but I'm not the only one who has reported this. Many of you have.

My hypothesis is that, yes, the material is breaking down, and contributing to the biological "load" of the system- but with an abundance of microorganisms living in, on, and among the botanical materials in the aquarium, and with regular frequent water changes, there is a very efficient processing of nutrients occurring.

This is purely speculation on my part, but I think it's as good a guess as any, based on the repeated similar results I've achieved in pretty much every single blackwater/botanical-style aquarium I've kept for the last 7 or 8 years!

I'm sure that a more sophisticated explanation, revolving around the presence of "on- board carbon sources" and other biological processes is the reason. I think that we're sort of looking at a freshwater equivalent of a reef aquarium in many respects, where, instead of "live rock", a lot of the microbial population and biological processes occur within and upon the surfaces of the botanicals themselves.

Almost like "biopellets" in a reef tank, perhaps the botanicals are not only a carbon source for beneficial bacteria- they're also a sort of biological filtration "substrate" for them to colonize on. Again, speculative, and needing some more rigorous scientific investigation to verify one way or another, but it's been my "working hypothesis" for several years.

In my opinion, once they get through the initial startup phase, blackwater/botanical-style systems seem to run incredibly smoothly and in a very stable manner. If you adhere to a regular, yet simple maintenance schedule, obey the long-established common-sense "rules" of aquarium husbandry, and don't go crazy with radical overstocking or trying to speed up things too much by dumping tons of botanicals into your established, stable tank in a brief span of time, these systems run almost predictably, IMHO.

And speaking of "maintenance"-  I'll concede that one of the "bummers" of botanical-style aquarium keeping is that you will likely have to clean/replace prefilters, micron socks, and filter pads more frequently. Just like in Nature, as the botanicals (leaves, in particular) begin to break down, you'll see some of the material suspended in the water column from time to time, and the bits and pieces which get pulled into your filter will definitely slow down the flow over time.

The best solution, IMHO, is to simply change prefilters frequently and clean pumps/powerheads regularly as part of your weekly maintenance regimen.

Remember, you're dealing with a tank filled with decomposing botanical materials. Good overall husbandry is necessary to keep your tank stable and healthy- and that includes regular water exchanges. At the very least, you'll likely be cleaning and/or replacing pre filter media as part of your routine, and that's typically a weekly-to bi-weekly thing.

Let's talk about the most dreaded of all aquarium occurrences: The appearance of  microalgae. 

While it would be intellectually dishonest (and just plain untrue) for me to assert that blackwater/botanical aquariums aren't susceptible to algae outbreaks, it is sort of remarkable that we simply don't have massive algae issues in these types of aquarium on a regular basis. I have to admit, that I have never had one of those nightmare algal blooms in a blackwater aquarium...and although it sounds like tannins or some other "substances" in the blackwater would be the obvious "x factor", I'll tell you that I've never had an outbreak in a clearwater aquarium, either.

So, from personal standpoint, I can shout, "My blackwater tanks don't have algae issues!" On the other had, none of my other tanks have had them, either. And I'll wager that neither have many of yours, as well!

Shit. Not helpful, huh?

I read a study from the University of Georgia, which tested the idea of algae growth in blackwater streams, to determine if the limiting factor was chemical (nutrient) or light driven...and lo and behold, the study concluded that it wasn't necessarily some magic stuff in tannins and blackwater, as much as it was light limitation! 

Yes, you heard me correctly.

Light-limiting effects of the blackwater itself were discovered to inhibit algal growth in coastal plain streams. As light penetrates the water, high DOC concentrations and suspended solids can scatter and absorb light, impacting algal growth significantly. 

Okay, sounds like a bummer if you want to believe blackwater is "magic", but the study also concluded that blackwater systems were somewhat nutrient-limited, which also affected the growth of algae- although this was not concluded to be the primary factor which inhibited algae growth. In fact, another study I perused about the Rio Negro concluded that it was found that there is a relatively small difference in "respiration rates" between "whitewater" and "blackwater" rivers, and that the presumption that blackwater systems are more "sterile" is sort of overstated.

Interestingly, the study also concluded that higher incidence of algal growth occurred in areas in Amazonia where water movement was minimal, or even stagnant, suggesting that, all things being equal, light limitation and water movement are possibly more significant than just higher nutrient concentrations alone!

And that makes sense, if you consider the long-held belief within the aquarium hobby that most plants don't do well in blackwater aquariums "because they don't get enough light!"


So the long-held aquarium attitude about blackwater having some algal-inhibiting properties is really based on the fact that it's...darker? I mean, every blackwater tank I have ever owned does have some algae present. Although, being a reef guy at heart, every aquarium I own has good water movement. I know that in leaf-litter-dominated aquariums, which I love, I still keep a good amount of flow going.

This is interesting, because you'd think a tank dominated by decomposing leaf litter would be a freaking "algae farm", right? And yet, I've experienced no more occurrence of algae in the leaf litter tanks than I have in other setups. On the other hand, regardless of what type of system I work with, I'm fanatical about husbandry and nutrient control/export...obviously, another key factor.

Interesting stuff, huh? And since a lot of blackwater/botanical-style tanks are hardscape, with little or no plants, the lighting we are employing is strictly aesthetic, right? So, you're not hitting a tank with decomposing pods and no plants with 14 hours of full spectrum light...Personally, I use LED, and I keep my intensity levels very low (as low as 15% on the low end to 20%-25% on the higher end). Aesthetics.

Well, that certainly can be part of the reason why this tank magically has essentially little to no nuisance algae, huh? We pin both the praise and the blame for algae on the wrong suspects, I think! 

Man, this deserves more study...a lot of it.

Let's think about algae in the aquarium to begin with...No, not the boring old "This is how algae problems happen in our aquariums..."  bullshit lecture that you've read on every website known to man since the internet sprung to life. You can find that stuff everywhere. Rather, let's think about how we, as a group, mentally are opposed to the stuff in our tanks.

I mean, yeah, I know of no one that really enjoys a tank smothered in algae. It looks like shit, and is a "trophy" for incompetence, in the eyes of most aquarists. In fact, I remember reading once that more people quite the aquarium hobby over algae problems than almost anything else.


Well, sure- algae problems caused by obvious lapses in care or attention to normal maintenance, like overfeeding, lack of water changes, gross overstocking, etc. are signs of...incompetence. The occasional algae outbreaks that many hobbyists suffer through have all sorts of other potential causes, and can often be traced to a combination of small things that went unchecked, and are typically controlled in a relatively short amount of time once the causative factors are identified.

Yet, as a group, us hobbyists freak out about algae in our tanks. I can show you a hundred pics of algae and biofilm covered logs in the Amazon and the Rio Negro and say, "See it happens here too! Natural!" and the typical hobbyist will still be rendered speechless with horror at the thought of the shit appearing in her tank!

And I can't even tell you what it would do to one of those "natural aquascaping" contest freaks or judges! People might die. You could be charged as an accessory to murder! Seriously.

So, not everyone gets it. Just like brown water.

Algae is the foundation of life, blah, blah, blah. Yet, it's also the foundation for a "cottage industry" of devices, chemicals, and treatment regimens designed to eradicate it. 

Regardless of what approach we take, natural processes that have evolved over the eons will continue to occur in your aquarium. You can fight them, attempt to stave them off with elaborate "countermeasures" and labor...or you can embrace them and learn how to moderate and live with them via understanding the processes by which they appear.

And the algae?

It'll always be there. It's just a matter of how "prominent" we allow it to be.

Back to the water exchanges, and what you should/could do during these sessions.

During my water exchanges, I'm merely siphoning water from down low in the water column. I typically do not remove the broken-down leaf and botanical material, unless it's becoming a bit of a nuisance, blowing into places I don't want it.  I don't remove leaves and botanicals as they break down. I'm a sort of "leave 'em alone as they decompose" kind of guy.

And I'm not going to go into all the nuances of replacement water preparation, etc. You have your ways and they work for you. It's not really "rocket science" or anything, but everyone has their own techniques. The one "constant" is to perform regular water exchanges in your botanical-style aquariums. Just do them.

Like almost any aquarium, botanical-style blackwater/brackish aquariums require attention, management, and maintenance. Water exchanges are important, like they are in any aquarium, providing the same benefits. Water testing is important, particularly in situations where you're starting out with soft, acidic water, as the impact of botanicals is far more significant in this environment. 

 For many hobbyists, water testing is a periodic thing, done on an "as I feel it" basis. Personally, I think the benefits of a more regular testing schedule yields a lot of good benefits for us.

Your testing regimen should include things like pH, TDS, alkalinity, and if you're so inclined, nitrate and phosphate. Logging this information over time will give us all some good data upon which to develop our expectations and "best practices" for water quality management. It's important for the hobby overall to document as much information as possible about how our botanical-style/blackwater aquariums establish and operate. This gives the widest variety of hobbyists the most reasonable set of expectations about these systems.

Remember, it isn't just about a new aesthetic approach. It's about a more holistic natural approach and methodology.

Algae, and the fears which accompany it, are not entirely unfamiliar to us. However, I think that if we take a more "holistic" mindset about it, we'll be in a batter position to deal with it.

So, before you siphon out that algae patch, pull that group of weeds, or  blast that Aiptaisa anemone with kalkwasser (for you reefers out there), pause for a second to consider why and how the "offending" life form came to be in that location.

And reflect upon how we can benefit by designing our aquariums to provide the optimum environment for each and every fish and plant that we treasure to grow and thrive. To give them every opportunity to do so is our challenge, and our obligation.

Stay patient. Stay diligent. Stay creative. Stay proactive. Stay consistent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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