I have a 130l Boyu tank, the all in one, with the chambers in the back, so there is no overflow, sump etc It does have a little skimmer. I have my spray bar angled up so it causes ripples on the surface. The spray bar is fed by a 1000l/hr pump which pulls the water through the chambers & then returns it through the spray bar. In addition have a Seio 620 (2400l/hr) in the tank. In the ripples the water appears fine, but where the water is calmer, I can see a film. How can I get rid of this & what is it ?