It is quite a few fish for a 30, but then again they are all smaller fish. I would be more concerned with them acting naturally and getting along with no agression because they are all in small tank and squashed, and some of them could be territorial.
The reason I say that is your water parameters seem to be in check. That is where I would really expect to see a degredation due to overstocking. I would start testing for phosphates just to be safe.
The film I think you can handle the film by adding flow...it really is just a surface agitation question. Even in the most pristine reef tank, if there is no surface agitation there will be a film (and there will also be a problem with gas exchange, which is really the basic concern here). true, this film may get worse if there is a heavy bioload like you have, but as long as it is not affecting your water quality, and as long as you can add powerheads to deal with it, then I don't think it is a huge issue. But I would definately get rid of the fiklm, not because the film is ugly, but because if you ahve a film, then odds are you are not geting enough axygen transfer at the surface...which is bad.
try the power heads and let us know if that works.
HTH
Stewart