I had a chevron tang back in the early 2000's that developed hole in the head. The tank he was kept in was spotless, I tried sheets of algae but he would never touch it. I ended up borrowing him to my LFS to place in there coral tank that had an algae issue. In eight months the tank was clean, and the hole in the head was gone. I took him home along with a new product the LFS started carrying, yep you guessed it Spirulina Brine. The hole in the head never came back and I have been a true believer ever since. However you get your fish to eat it, Spirulina is a must.