IME, white film is from debris in the air. During dry season my water quickly builds this film but not in the wet season when it's extra humid. Once fry are free swimming you could set air pumps to 1 bubble per second or two - this will reduce the film. And when fry are bigger, set the pumps at a stronger rate.
When you do water changes try scooping out the surface of the water as well as the bottom. If the film gets too thick, dip a bottle in it and slowly pick it up. The film will stick to the bottle.
IMO this film isn't harmful as long as it's thin.