I don't know if it's the same thing or not, or if this will help or not, but my tanks get a film on the top when I don't have sufficient surface agitation. If I make sure my filters are stirring up the surface of the water sufficiently, I don't get a film. On my 10 gallon tanks, with a whisper 10 filter, there is so little surface agitation I get a film occasionally. It bugs me, so I'll run an airstone in the tank for little while to clear it off.