sounds like your peppermint shrimp is having a serious case of the munchies. I have had mine decide my yellow colonials were the tastiest things ever and blaze back half the colony before I caught him. that's the best opinion I have have on it. if you have a QT tank throw your peppermint in there and see if your polyps show signs of recovery. I do know that if you don't find a solution soon they probably wont last much longer, maybe a month.