Can you give us your test results for:
Temp
Salinity
PH
Ca
KH
Ammonia
Nitrite
Nitrate
Phosphate and Magnesium could help, but we'll start with t he basics.
Also, are you feeding the coral at all? Some LPS can benefit greatly from even occasional feedings.
Also watch out for nearby corals, etc that may be stinging at night. Fish and other critters may be harassing it as well.