Stubborn Protein Film

[Snaz]

I don't know if this is your problem but I will describe my surface film problem and how I solved it.

The toothed overflow gate where the water exits the main display had "teeth" that were too long and as a consequence the water did not flow out via the surface of the display but just under it. The solution was to block off the lower half of the teeth with some flat plastic from a CD case which forced the water to truly leave the display from the surface. Beware this will raise the water level in your display.