Birdsnest dying?

Hi I've had this pink birdsnest for a couple of weeks and recently my flame angel has started to pick at it and the birdsnest doesent extend it's polyps anymore in the day and it's turning white in the lower and middle parts of it, is it dying or bleaching and I do plan on getting the angel out of the tank because he nipped at my green montipora so bad the skeleton is starting to show. Help would be appreciated thanks