Surface film it caused from lack of breaking the surface. You need to break the water's furface to keep the film from forming. Simply directing a pump or 2 upwards to chop up the surface and it will prevent the film from settling. forcing the film to move around unitl it fines the overflow. I have a great deal of surface film in my sump but I can easly net it out, better in the sump than the main display.
Sorry I've been working very long hours & weekends, I still have the leathers and shrooms, If I don't work this coming weekend I'll give you a call. I work 3rd shift so it would be after noonish time, If I don't have to work that is.