the reason i asked about the lights is that if we assume you don't have any chemicals in the tank and we assume the tank has cycled, then something has to account for the death of the coral but not the fish. if the lighting was really poor that could account for the death of the coral but not the fish. however, the lighting seems more than adequate, so at this point i'm going to second Christopher's thoughts on the iodine. it may have seeped into the rocks and is leaching out into the water.