Are you using CO2 at all? I know some liquid CO2 stuff causes a film on the surface.
Also, what filter are you using? If it is strong enough it should be able to agitate the surface and break it up.
I don't have much experience with this, but I'm sure other members do. Hopefully you find a solution soon!
I do not use CO2
and thanks for all the input, i did use a sponge and cleaned it but i was curious of what it might be, and how i could prevent it.