i had the same issue, my corals were fine then all the sudden they wouldnt open. half mine bleached them selfs out or something being closed up for so long.
i dipped all mine i had to cut allot off of the rocks, most my rocks are huge and i couldnt move them. but after dipping they are great you would be amazed how much stuff is living on you corals you dont see that hurt them. sucks having to take them off rocks but amazed how fast the opened up.