Algal praise?

As aquarium hobbyists, we're sort of "programmed" to freak out about the appearance of algae in our systems, aren't we? It's like the "default" to go "ape-shit crazy" when algae appears in our tanks.

I haven't touched on one of the more interesting "benefits" of a botanical-style blackwater aquarium that many of us have experienced: The fact that the occurrence of nuisance algae outbreaks seem to be relatively uncommon in these systems.  Not a rarity- just not all that common. 

Or, is it?

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. At least, none that anyone talks about!

I have to admit, that I have never had one of those nightmare algal blooms in a blackwater aquarium...unless my goal was to intentionally create one. And of course, in the interest of pushing the state of the art of our practice- I have succeeded at creating some algal blooms!

Yea, I did. And, as you'd imagine, it's not all that difficult. Blast the damn thing with light, and, well, yeah. Algae farm.

I mean, algae likes "fuel", right?

Our tanks feature a lot of botanicals and their associated materials decomposing on a near-constant basis.  As we know, some of this material is utilized by fishes for supplemental food. Some of it is processed my crustaceans, bacteria, fungi, and other microorganisms. And yeah, some of the compounds produced by it as it decomposes (nitrates, phosphates, trace elements)  is utilized by algae.

I rather fancy the stuff, actually.


And the simple fact is- algae will bloom and proliferate wherever and whenever the proper conditions- nutrients, light, flow, and lack of heavy consumers- combine in the aquarium environment. And quite honestly, it's not that amazing, right? We know this.

 Yet, when we have darkly tinted water and maybe not a ton of lighting over our tanks, it seems just a bit less common- usually!


And of course, Nature provides the example.

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! 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. You'll often hear that depressed CO2 levels are instrumental in creating algal outbreaks, like the dreaded "black beard" algae.

Good flow is important. You don't have to have a wicked, jacuzzi-like flow. Just good, steady, movement and a bit of surface agitation.

This whole thing about even being able to limit nuisance algae in our tanks is interesting, because you'd think a tank dominated by decomposing leaf litter would be an algae farm, right?

And yet, I've experienced no more occurrence of algae in the leaf litter/twig substrate 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.

And since a lot of blackwater/botanical-style tanks are "hardscape only", with little or no plants, the lighting we are employing is typically strictly "aesthetic", right? So, you're not blasting a tank with decomposing pods and no plants with 14 hours of full spectrum light...Well, that certainly can be part of the reason why this type of tank often "magically" has essentially little to no nuisance algae despite all of the leaves and stuff, 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.

And with more and more hobbyists playing with planted blackwater tanks, we'll have a greater "body of work" from which to draw. For that matter, more botanical, blackwater tanks in general means more material to analyze! 

An here is another thing: As we've beaten into your head relentlessly, in our truly "natural style" tanks, we don't really care if there is some algae in there. We've made that "mental shift" that says it's okay to have some decomposing botanicals, brown water, biofilms, and yeah...algae. Because natural habitats do, too. So it's not so bad, right?

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..." lecture that you've read on every website known to man since the internet sprung to life. Yes, it smothers plants, which sucks if you like plants. You can find all of that 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 crap, 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 matrixes 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.

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! 

Do you want that on your conscience? 😆

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. 

I say, we can embrace it and understand why and how it forms and proliferates...and even embrace it for being an elegant- if aesthetically under appreciated- part of the botanical-style aquarium.

So, the round-about conclusion here is that:

1) Although there are many beneficial substances in blackwater, such as humic substances, tannins, etc., it's inconclusive if they alone are the reason (or even part of the reason) why we seem to have less incidence of algae in our blackwater aquariums. Some research suggests otherwise.

2) The light penetration limitation imposed by blackwater definitely has been shown to decrease algal growth.

3) Proper nutrient control and export mechanisms employed by the hobbyist can go a long way towards controlling excessive algal growths in the aquarium.

Okay, maybe not altogether earth-shattering revelations...Yet, important points to consider.

Yeah, we have a lot of work to do when it comes to understanding all of the dynamics of the "algae equation" in botanical-style aquariums.

Stay curious. Stay diligent. Stay engaged. Stay thoughtful...

And Stay Wet.


Scott Fellman

Tannin Aquatics



Scott Fellman
Scott Fellman


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