# Surface biofilm best practice?



## ObiQuiet (Oct 9, 2009)

I've read Diana W's article on Mycobacteriosis in Aquarium Fish about EM (environmental mycobacteria) and am of course aware of the point about gas exchange and surface agitation.

I'd like to fill in some holes in my understanding about how to best manage the surface biofilm, so thought I'd ask!

There are two, maybe three reasons to remove or reduce surface biofilm:
* We don't like how it looks
* "EM are found preferentially at the water surface and in biofilms" (D. Walstad)
* It interferes with beneficial gas exchange (?)

There are a few methods:
* Remove the surface biofilm (e.g. with a pitcher, paper towel, etc)
* Skimming the surface as part of intake to a mechanical filter
* Surface agitation without filtering (e.g. air bubbles, waterfall output)
* others?

Questions:

1. Grant that each method can be done to greater or lesser degrees. Might one be able to find a balance between enough surface agitation to control biofilm but not so much that CO2 loss is significant?

Note: Given what Ms. Walstad reports about aerosolized EM, bubbling and sprinkling would seem worth cautioning against. Which leaves me with:

2. Does skimming the surface into a filter help enough with EM baterica levels, or does the biofilm have to physically leave the tank instead of being broken up?

Thanks for any discussion, clarification or new points!
-Obiquiet


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## Gerald (Mar 24, 2008)

"Does skimming the surface into a filter help enough with EM baterica levels, or does the biofilm have to physically leave the tank instead of being broken up?" I'm mostly just guessing here, but I dont think breaking up the film with air or turbulence will reduce numbers of EM bacteria - they'll just get dispersed around. I use the paper towel trick if there's a visible slick I want to get rid of.


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## ObiQuiet (Oct 9, 2009)

Gerald said:


> I'm mostly just guessing here, but I dont think breaking up the film with air or turbulence will reduce numbers of EM bacteria - they'll just get dispersed around.


I'm sure you're right. Removing the film from the tank will reduce the numbers, keeping the film from forming or getting thicker may reduce the growth rate of the bacteria.


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## mysiak (Jan 17, 2018)

I am using gentle surface agitation - I see small ripples, but no splashing. Duckweed and maybe other floaters seem to be somehow removing this surface film, but agitation is extremely easy to do and very effective.


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## mistergreen (Mar 3, 2007)

I've found it most effective to have fish eat the biofilm. Livebearers and gouramis eat them.


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## Michael (Jul 20, 2010)

Though aware of mycobacteriosis, I've regarding this primarily as an aesthetic problem. On my large tanks I use small skimmers made by Eheim. These take any surface film or debris through a small sponge. The sponge becomes clogged and is removed and rinsed. So the skimmers do physically remove any film.


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## dwalstad (Apr 14, 2006)

Removing biofilms entirely with paper towels, surface skimmers OR skimming oily slicks during water changes is ideal. Dispersing the biofilm into the bulk water with surface agitation is certainly better than allowing fish to eat the biofilm and getting a mouthful of mycobacteria.

Mycobacteria enter the fish via the digestive track, so surface-feeders eating the biofilm itself is not a good thing. The greater the number of mycobacteria entering the digestive tract, the worse off for fish. Healthy fish can handle small numbers of mycobacteria, but large numbers concentrated in a biofilm could cause disease problems.


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## tiger15 (Apr 9, 2017)

The cascading flow pattern of hobs will disperse the surface film.


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## ObiQuiet (Oct 9, 2009)

Thanks for the discussion, everyone.

Perhaps it comes down to this:
* If there is a surface biofilm, it's best to take it right out of the tank.
* Skimming and dispersal are not the best ways to get rid of an existing biofilm layer, as those leave the MB in the tank. (With a skimmer, water is even pumped through and past the biofilm -- not ideal?)

* There are many ways to prevent biofilm growth, which reduces the environment for MB to grow in.
* Any of the surface disruption techniques will work for this.


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