Like everyone has said it is most likely bleaching, a list of your parameters would also be of great help so we can determine if it is in fact the lighting or if something else with your water is stressing it out.
I spot feed all of my LPS 3x a week with meaty foods including silversides, squid, table shrimp and also I feed brine shrimp cyclopeeze and prime reef flake every now and then. I thaw it out then about 15-20 minutes after my main lights go out, so just the actinics are on, that's when I feed. I suck up the food into a turkey baster and lightly spray the food over the tentacles of my trumpets, candycanes, pineapple brain, frogspawn, fungia plate, hairy mushroom and rics. Hope that helps your "feeding" question.
Good Luck and Happy Reefing,
Brianna:rollface: