# oil slick surface agitation and O2 exchange



## davec (Jan 19, 2010)

I have an integrated overhead filter which causes next to zero surface agitation. Which allows a thin film of oil to cover the surface which I assume is normal. I noticed a week ago that the cardinal tetras were also gasping near the surface in the am (which I assume is the nadir dissolved O2 in the water since the plants were not photosynthesizing overnight and were using O2 themselves). I initially thought it was d/t ammonia nitrites. Readings were OK so I just turned the aerator and within minutes the cardinals seem to be happy again and I didn't lose any.

So the question is how do you get rid of the oil slick. I've heard paper towels being used. However I assume that there is fat from the fish food itself. Therefore, do people with canister and subsequent low surface agitiation run their aerators continuosly to oxygenate the water and disrupt the surface and live with the additional white noise?


Thx


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## Darkblade48 (Jan 28, 2008)

The oil slick that you are noticing is indeed normal, and is usually caused by excess proteins (i.e. from fish food, as you have mentioned).

Paper towels do work, but can get quite tedious quite quickly. What most people do is to aim their spray bar (I am not sure what an "overhead filter" is, so adjust accordingly) so that the surface of the water is rippling. This way, sufficient agitation is present to break up the surface scum, but not enough to diffuse out CO2.


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