Hole in head

[SHowald72]

My powder brown tang has a big hole in his head. It is right between his eyes and down to the bone. He did not have this last night and shows no other signs of stress. He is eating and swimming around as if nothing is wrong. The hole goes all the way across from eye to eye and looks as if something was eating his face. The fish is in a reef tank, so no hope of catching it. Any suggestions on what I should do or what may have caused this.

 

[Sk8r]

HLLE: head and lateral line erosion. Best I know, water quality and good nutrition are the best treatments. What's his diet?

 

[SHowald72]

water is good. Diet is reef flakes by ocean nutrition and frozen food occasionally.