White Film In Betta Tank. There are several causes of white or gray water in cloudy fish tanks. This white or oily film that forms on top of your tank’s water is usually a bacterial bloom.
Below is a picture showing what this algae looks like in a fish tank I have 2 tanks, one is a 2.5 gallon with one male betta. My tank has this film and i am running a canister filter so there is water movement.