Hi @MichaelJ & Everyone,Hi @saundersbp I agree and I would take it a bit further and claim that we pretty much always have varying degrees of surface film in our tanks. It's only when we have too much of it it's an issue... the origin of surface film (usually made from protein/fat compounds) is food decay, waste from livestock among other things.
I'd like to add one other source of surface film - the aquarium plants themselves, assuming that it is a planted tank. 🙂
JPC