Both my clowns take turns hosting my frogspawn and open brain coral. Both corals are fine and this has been happening for over 1 year now and no ill affects on either coral. It is real funny seeing a cown fish laying on top of an open brain, first time I saw it i thought my clown was dead lol. One is now starting to go into my torch. At first I did see marks on the fish but after a while no more marks, not sure if they become immune to it.