if they are infact clownfishn you have no worries of them eating corals. also clowns have been known to host in corals and sometimes in bubble corals maybe you mistook what they were doing.
Amphiprion bicinctus are know as the two banded clownfish. If it is one of these then I wouldn't have thought that it would eat corals. Saying that though, Saltydunc has a Powder Blue Tang that are supposed to be Reef safe and it's totally chomped through his leather coral. You just never know with these darn fish.