nice sun coral, looks really healthy, a bit of dead tissue seems to be normal, mine had about that much when I bought it. they normally open up at night for feeding, interduce a bit of food at lights out and they should start to open, then feed them. they will get use to being feed in the evening, mine have gotten were they start to open even before the lights start to dim. I usually feed about three times a week. and have a lot of new growth.