If you can, I'd do a 50% change. That will impact the NO3. The temp will contribute to the film algae a bit, but it's there for mostly the same reasons as the brown is in the corals.
That should clear up a bit once the other issues are settled.
I feed quite heavily (I guess that's subjective
) and don't have issues, so more of a nutrient management process. A great skimmer helps. Maybe smaller more frequent feeding? Or, if you're really dumping it in, back it off a bit.