The airpump is to improve oxygenation, at higher temperatures you'll want to do everything you can to get O2 into the water, surface agitation is the key there. Filter outlets by the surface and any powerheads pointing up to the water line will do the trick though. Anything to get the water at the surface moving around once the temp gets up high.
Gills might be red because of the stress from the whitespot, might be a sign of why the fish got stressed. Have you checked the other parameters? Would be interested in knowing what the nitrite level is in there with that look.