This is a recent development. My coral beauty angel has the same raw looking area on both sides if the body. It started out looking like another fish had nipped it but it keeps getting bigger He is eating fine and seems to behave the same as always.
I have a 65 gal
w a 20 sump the tank parameters are all zero nitrate nitrite and ammonia my ph has been a little off I'm checking it daily to get it back to 8.3.
There are 3 chromis a clown a box fish a long nose hawk and a sailfin tang w my angel. There are a few feather dusters and the Kenya trees
Any help would be appreciated