I have an Achilles tang that's been in my display tank for 8+ months. I came home today and noticed the right side of his face had something very wrong. I've never seen anything like this before and was wondering if someone could help ID what the heck this is. I pulled him out of the display and have it in a 10 gal QT with some antibiotic powder to see if this will get him better. Any advise is appreciated.