Yeah, that looks way overstocked. The problem is that if it is Ich, its in the tank now and other fish can get it. Its got all sorts of hosts too, so its not going anywhere. That size with that many fish is going to be near impossible to treat properly. I don't see throwing that many fish in a QT and with all the corals, you can't hypo the DT. Try to maintain pristine water parameters (which has gotta be tough being so overstocked), keep the tank as stress-free as possible (again, near impossible when overstocked) and try to keep the rest well-fed and healthy so that they can possibly fight it off.