I have tried both of what was posted none have worked. I have 2 pumps breaking surface and a protein skimmer yet still have a film... following along...
More info about your system? Is it an overflow/sump system or is it maybe HOB or canister filter?
I'm sumpless, one tank uses a HOB filter and the other a canister. I used to have a slight surface film but fixed it with a filter intake attachment that skims water from the surface. Just like this one:
But if you have an overflow to sump setup, I can't imagine how a surface film can develop. It should all be going over the edge.
When I had a film of cyno on my surface of the water. I took a power head and let go close to the surface so it sucked some air and it got rid of the fil in a hr never came back I increased flow with a dual power head and the single power head I have breaks the surface it just doesn't airate it anymore.