what causes "protein film"? - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 5 Old 10-30-2011, 09:48 AM Thread Starter
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what causes "protein film"?

On my previous tank (23 gal), I had added to my AC30 a small Penguin biowheel, and the film on the top of water was gone. I've since put my fish in a 30 gal and just have a AC70 on the tank. I see the film is back! Even though there is plenty of water movement. What causes this? Is it harmful? What can I do to get rid of it, short of buying a protein skimmer (which I have no idea what that is)


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post #2 of 5 Old 10-30-2011, 10:00 AM
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The best I understand it comes from the biological makeup of the tank. Some tanks have them others don't. In my 29 gall I don't have it. I had some for awhile in my 55 gallon tank (still do but it is very little now). As for the things to do about well my understanding surface movement will help with this some. Is it harmful to the fish? I don't know but if left unchecked I think it can cause problems with gas exchange. Though with the HOB you have that should be an issue with the surface movement you are probably getting. Another thing is light if the film is to think it will be hard for the light to get through. I would siphon it out the best you can during water changes every week. One thing I have done in the past is taking a paper towel and pulled it across the surface of the water to pull the film off/up just sure it is a plain paper towel though.
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post #3 of 5 Old 10-30-2011, 11:52 AM
Have you ever noticed the eddies around a waterfall. The waterfall injects a lot of air into the water. The bubbles carry suspended organics into a foam that gets captured on the surface. This is essentially what a protein skimmer does. The suspended organics get trapped in the bubbles and get extracted from the water.
A protein skimmer requires a tank overflow, sump and is pretty expensive.

You might resolve more simply by just providing more surface agitation - perhaps something as simple as an air stone or bubble wand would do the trick. Before that, you might change the frequency and/or amount that you feed your fish as it may simply be excess food that's causing the surface slime - ?


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post #4 of 5 Old 10-30-2011, 07:05 PM
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I concur with Boredomb's explanation, and I agree with AbbeysDad's comments. One other method is a surface skimmer attachment that you can get with many canister filters; I realize you have a HOB, so that is not an option in this particular case. I have used the surface skimmer with my canisters, but small fish kept getting pulled in and stuck, so I took them off. Making screens I didn't want to do because then floating plant bits get caught and the thing doesn't do its job.

Obviously if I had these gadgets I must have had protein scums. As has been mentioned, they are basically harmless unless they get bad, and I have had that in one tank. Excess organics cause this, similar to cyanobacteria. And interestingly, in tanks with bad protein scum I also had significant cyanobacteria. Not really surprising, considering.

Slight surface disturbance usually keeps the protein scum very minimal. It is frankly just another part of a natural system. I see it more in some tanks than others. Remove what you can during the water change by inverting the siphon and skimming the surface manually.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #5 of 5 Old 10-30-2011, 08:00 PM Thread Starter
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Thanks to you all for the input. It's very minor. I'll try the suggestions of getting it off during water changes. As long as it's harmless. It's just a very thin film over the water,nothing more at this point. I hate to add another filter, as I think it's just too much water movement. My AC is on the lowest setting, but that seems appropriate given it's a AC70 on a 30 gallon tank.


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