I am by far no professional, but what worked for me was buying a small tank, something cheep with at heater, and put the fish in that. I put my yellow tang and my fire fish in a 1 gallon tank for a week. I used OuIck Cure by AP. The main ingredient Formalin. What ever you do, do not put this product into the main tank. I did a small water change ever day like half a gal
, and used another product called Ammonia Safe, because of the small size of the tank, the ammonia was high. I just didn't have the money at the time to buy a bigger tank. Now this sounds crazy, but I only did this because he was really bad. Within two days, he was clear to the eye. I treated him for a week, along with my fire fish and they both survived. Good luck.