I dunno what it is but it happens to me when the filter is not moving the water on top as much. What helps me get rid of them or make them less noticable is having some floating plants like duckweeds etc... and the film just "dissapear" in my tank see if you can get some floating plants
don't think so, like laki mentioned, could be from leftover food from b4 or just random stuff in the air it just looks annoying. you could try to remove it with a small betta cup it'll get rid of some. How thick is the film? does it look oily (colorful)
I have marimo moss and java fern. In the tank with the big mama java fern (and all 7 babies) the film is not as bad.. In Ludey's tank (he just has moss, no java yet) the film is thicker and goes much faster after feeding.