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What kind of "film" are you talking about? I believe certain chemical additives will add what appears to be an oily looking film under certain circumstances (e.g. too much of the chemical such as Stress Coat dumped in the tank, not enough surface agitation, etc.) on the surface of the water that will dissipate over time. When I added Stress Coat I got a little film but it went away after a day or two with no ill effects. If you are worried in the short term though you could always take a paper towell and lay it on top of the film and soak it up. You will have to identify the root cause though.
I have a 35G swim-thru tank. (Imagine 2 x 27G tanks up on end, 7" apart, connected by 2 5" diameter tubes). I have a Fluval 304 canister filter with the output in one tank and the intake in the other. The output side had plent of flow, but the intake side always had a film.
I attached a surface skimmer to my intake side and it fixed the problem.
A surface skimmer connects to the intake of your power filter and is positioned on the surface of the water. As your filter draws in water it draws it from the surface. (You can adjust it so it draws from the bottom/top or a combination of both).
Basically, they remove organic film on the water's surface and help to improve oxygen exchange.
Here's what they look like... http://www.geocities.com/myfishtank2001/skimmer.htm