The film is a collection of proteins, as mentioned above there can be several reasons for them but without knowing your setup it’s hard to give a useful solution. It can be as simple as directing a pump/powerhead toward the surface to help them down an overflow to a skimmer to remove them, back in the good ole days before skimmers we used news paper to remove them.
I use a pump that turns on every hourish that pulls in air, creating a mist of bubbles. I run it for about 2-3 minutes. I am unable to easitly set up an overflow on my tank.