A "refresher" on biofilms and the creatures who love them.


Even the word conjures up an image of something that you really don't want in your tank. Something dirty, yucky...potentially detrimental to your aquarium's health. 

And, let's be honest with ourselves here. The damn dictionary definition is not gonna win over many "haters":

bi·o·film -ˈbīōˌfilmnoun -a thin, slimy film of bacteria that adheres to a surface.
Some charming and commonly-encountered examples of biofilm include  plaque that forms on teeth, and the slime that forms on surfaces in water.
Shit. Really?
Yeah, I guess that's the definition we have to run with.

Well, apart from the unpleasant-sounding description of the stuff, the concept of biofilms and how they form is actually kind of interesting. Not "charming." I didn't say that. But interesting for sure.

Biofilms form when bacteria adhere to surfaces in some form of watery environment and begin to excrete a slimy, gluelike substance, consisting of sugars and other substances, that can stick to all kinds of materials, such as- well- in our case, botanicals.

It starts with a few bacteria, taking advantage of the abundant and comfy surface area that leaves, seed pods, and even driftwood offer. The "early adapters" put out the "welcome mat" for other bacteria by providing more diverse adhesion sites, such as a matrix of sugars that holds the biofilm together. Since some bacteria species are incapable of attaching to a surface on their own, they often anchor themselves to the matrix or directly to their friends who arrived at the party first.

Sorta sounds like Facebook, huh?

(The above graphic from a scholarly article illustrates just how these guys roll.)

And we could go on and on all day telling you that this is a completely natural occurrence; bacteria and other microorganisms taking advantage of a perfect substrate upon which to grow and reproduce, just like in the wild. Freshly added botanicals offer a "mother load"of organic material for these biofilms to propagate, and that's occasionally what happens - just like in nature.  

Yet it does, so we will! :)

Is there a "darkside" to biofilms? Of course.

Like anything else, too much of a "good thing" can cause problems in rare instances. Frightening, "aquarium armageddon scenarios" could play out. For example, in an extremely overcrowded aquarium (or a very small one) with marginal husbandry and filtration, with a huge amount of biofilm (relative to tank volume) caused by an equally huge influx of freshly-added botanicals, there is always the possibility that bacteria within the biofilms can multiply extremely rapidly, reducing the level of oxygen in the rest of the aquarium, which could lead to a dramatic reduction of CO2 being released out of the water. This, in turn, could lead to CO2 levels rising quickly and sharply, potentially causing asphyxiation to the animals in the tank- including the lovable nitrifying bacteria that support it.

Now, that's a true "doomsday scenario"- brought about by a non-sustainably-managed/populated aquarium, improper preparation and rapid, excessive additions of botanicals, and complete lack of common sense on the part of the aquarist, in terms of husbandry.

So yeah. There IS a darkside to biofilms. If you create circumstances to foster one.

The real positive takeaway here: Biofilms are really a sign that things are working right in your aquarium! A visual indicator that natural processes are at work.

Yet, understandably, it may not make some of you feel good.

First off, take comfort in the fact that this is typically sort of a passing phase, and can take anywhere from a few days to 2-3 weeks before it subsides on it's own to some level that you can live with. Realize that biofilms are present in every aquirium, to some degree. Yeah, even your "Nature Aquarium", guys. Welcome to Planet Earth.

We get it, though- some of you just don't want this stuff, despite its "charms."

Okay, well, when you've got a lot of this material in your aquarium, and it's causing you considerable worry, stress, and just plain giving you a case of the shivers, there are some actions you can take ( besides cursing the whole idea of throwing aquatic botanicals in your system in the first place).

What to do? Here are a few time-tested options:

  • You can wait it out. That's right. Do nothing, except appreciate the wonders of nature, no matter how unsightly they may be at times. I mean, didn't nature make the "Death Flower" and the "Slime Mold?" Seriously. Yeah. And this is nicer to experience than "terrestrial" biofilms, like, oh, let's say... plaque!


  • You can remove the offending botanicals, give them a good scrub with a soft bristle brush (like an old toothbrush), a rinse in fresh water, and put 'em back in.


  • You can remove the botanicals, give them a good scrub, and re-boil/soak them again. Although a bit redundant, and in our opinion, not necessary, this procedure does have the advantage of removing some of the trapped organics that lead to the initial "outbreak", but you may see it happen again.


  • You can leave the botanicals in place, and employ some natural "control", in the form of ornamental shrimp. Yeah, that's right- your "Crystal Red Shrimp", "Bee Shrimp", and the rest of those tiny, overpriced, yet engaging little crustaceans  absolutely adore biofilms, and will attack it voraciously. Alternatively, we've learned that some fishes, like Plecos, some Corydoras cats, and even Leporinus and other "Headstanders" seem to pick at this stuff fairly aggressively. In fact, I've seen Pencilfishes and other small characins pick at it.


Again, the reality here is that in an otherwise well-managed, sustainably-populated aquarium, at best the largest blooms of the stuff will be a temporary nuisance, subsiding to a tolerable level, or even being almost unseen, for as long as you have the aquarium in operation.

Remember, it's all part of the game with a blackwater, botanical-influenced aquarium. A part of that "mental shift" towards accepting and appreciating a more truly natural-looking, natural-functioning aquarium. The "cost of admission", if you will- along with the tinted water, decomposing leaves, etc., the dues you pay, which ultimately go hand-in-hand with the envious "ohhs and ahhs" of other hobbyists who admire your completed aquarium when they see it for the first time.

Now, there are a lot of you who have come to admire, and even love the whole idea of biofilm. Like, those of you who love the aforementioned ornamental shrimp. You understand the value of having a periodic "crop" of this stuff available for your shrimp to "graze" upon. You actually are wanting to foster it. 

So, what are the botanicals which seem to give you the best shot at purposely "recruiting" the stuff? Well, pretty much all of them- in fact, almost anything you put underwater- will recruit some biofilms at some point. However, in our experience, there are a few which seem to "recruit" more biofilms initially than others. They are:

"Teardrop Pods"- which also tend to soften more quickly on their interior than many other botanicals, rendering them more attractive to biofilms in the early phases of their "run" in an aquarium.


Magnolia leaves- Yup, these most beloved, tannin-imparting leaves have that waxy "cuticle" that seems to recruit biofilm more quickly than other leaves during their first weeks of submersion. It seldom lasts very long, generally subsiding dramatically on it's own quite fast. 

"Concha Pods"- Another lightweight botanical with an interior that seems to soften very quickly, recruiting a good amount of biofilm in the process. Like the "Teardrop Pods", the biofilms tend not to linger very long, so "make hay while the sun shines" and let your shrimp have at 'em quickly!"

Jackfruit Leaves - These Indian leaves tend to be attractive to shrimp anyways; however, with the "value added" benefit of rapid biofilm recruitment, your shrimp will feel like you really appreciate them, and no longer any harbor resentment for the shrimps' ridiculous $400USD per gram price tag. (sorry, couldn't resist!)

Now, you may have other favorites for this purpose, and we could probably devote a whole damned article to it (Why not, I've just written a thousand-plus words on biofilm! Where else in the aquarium world are you going to find that kind of content every day- for free, nonetheless? And yet, some of you still buy generic, "non-romanced" Catappa leaves from some clown on E-Bay. Really? Huh? How DO you sleep at night? Have I guilted you yet?)

Okay, this is getting a bit "long-winded", and even a bit nasty- but you get the idea. Biofilms are  common in nature, and a part of pretty much any aquarium, yet a bit more significant (and noticeable) when you play with aquatic botanicals. They are not to be feared- although they should be respected- and ultimately, utilized as food by your animals!

Stay calm.  Stay brave. Stay curious. Stay devoted.

And Stay Wet.

Scott Fellman

Tannin Aquatics



Scott Fellman
Scott Fellman


9 Responses

Scott Fellman
Scott Fellman

September 24, 2020

Nothing to fear, Laura! Glad you made the shift!! Opens up all sorts of incredible possibilities!


Laura Ashton
Laura Ashton

September 23, 2020

Many thanks! My brain has made the appropriate shift and I can now consider the biofilm growing on a new piece of driftwood as friend not foe!

Scott Fellman
Scott Fellman

May 13, 2020

Hi David!

I’ve never even heard that one! Once again, I think it’s an “aquarium myth” sort of thing- “The wood is still producing biofilm and fungal growth, therefore it’s not ’cycled!” Or something like that. I think it’s a semantic thing. Wood is “cured.” Botanicals are “prepped.” What does that mean? The wood has stopped leaching tannins? It’s staying submerged? NO longer producing vast quantities of fungal and biofilm growth? What does that mean, and what’s it have to do with a “cycled” tank? Yeah, don’t be fooled by this line of thought. Just because something looks different than we want it to doesn’t mean it’s not healthy, safe, stable, etc.And since when do visual cues trump water testing to determine when a tank is cycled. The appearance of biofilm likely has nothing to do with wether or not a tank is “cycled.” We must monitor the water chemistry to make such determinations. IS there ammonia or nitrite in the tank? The fact that you have fungal growths or biofilms means that there are some bacteria present, right? I’m not sure how that one got started; it’s often frustrating to hear those kinds of things.


David Thorpe
David Thorpe

May 11, 2020

Thank you for shredding the prolific myth that biofilm is an iron-clad sign of a tank not being properly cycled. I have a sizable chunk of grape wood loaded with it – about 1 cm thick. The Nerite snails and Panda Cories love the stuff.

Scott Fellman
Scott Fellman

November 21, 2019


Well said! I wholeheartedly agree…


aidan garrity
aidan garrity

November 20, 2019

having a tank with no biofilm is like having a forest with nothing but birds and mammals

Scott Fellman
Scott Fellman

April 22, 2019

I agree! There seems to be so much concern about biofilm as some sort of “problem”- when the reality is that it’s more of a “gift” from Nature! We just need to mentally shift from being freaked out by its appearance and what we THINK it represents…rather than getting excited about what it offers!


Karin Raymond
Karin Raymond

April 20, 2019

Guppies and their fry devour biofilm!

Lori Bowman
Lori Bowman

March 16, 2019

I find the best cure for biofilm is have more animals that love to eat it. Most fish and invertebrates are healthier when eating live foods. Biofilm is very much alive. Beneficial algae seem to like it, too. Shrimp, snails and fish like ottocinclus will have a feast! When the animals are healthy their behavior is much more lively, natural and interesting. With all the activity the entire tank is more fun to watch even if your main concern is plants. My advice is let the biofilm be. It won’t be unsightly for long. Something will come along that loves the biofilm more than you do.

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