If they are melting away it is a fungus. I have had this a few times just blast away all the dead tissue couple times a day so it doesn't build up. You will lose a lot of polyps but they will recover. I just went through this with my AI red zoos I had a huge colony that started to slime over, twice a day with the turkey baster and they recovered. Lost half the colony though
. Make sure you do all the zoo cause it can spread.
HTH