Also make sure that you have lots of water movement in your tank with turbulance on the top to encourage oxygen saturation. If you don't already have a good skimmer hooked up you might want to consider that.
You have a lot of fish in your tank so unless it is well oxygenated (sp) you are going to have problems. My blonde Naso was the only large fish that managed to survive when I lost circulation overnight due to a tripped breaker but he was not looking good the next morning - blotchy and breathing extremely laboured.
I hope you are planning a tank upgrade soon if you plan on keeping all those tangs.
