Problem with Zebrasoma desjardinii-Please Help!

[revgeoff]

My Red Sea Sailfin tang didn't eat last night...considering he is always the first one in I thought that strange. Now he is at the top of the tank and occasionally sticking his mouth out of the water.
Normally this the sign of:
1-lack of air circulation. I have two seios and the return from the sump. Nobody else is acting strange either (although he is the largest at 6 to 7 inches).
2-high temperature...temp is at 81
3-airtight covering stoping gas soubility...sump is not covered and although the top is glass covered there is still a several inch gap at the back.
4-parasites in the gills...these look fine as well.

I changed the lights to 2x175w mh from the pc lighting I was using, and I have just performed a 20% water change on the 120 gal tank. No new fish have been added in some time and as I stated above, nobody else is acting strange.

Does anyone have a suggestion? I really really don't want to loose this fish!