Help needed to save a hippo tang

4 days ago my hippo tang developed what appeared to be ick after being in my
reef tank for almost 6 months. She is now quarintined with her tank mate, a
percula clown fish who has showed no signs of infestation. Initially I did a
freshwater bath and placed them in a small tank with a
cooper/formalin/malchite mix to treat them. On day 2 the hippo tang looked
better and was feeding. Suddenly on day 4 the hippo is now covered with what
appears to be ick and now also has clouded eyes, the percula looks fine.
What am I doing wrong? Urgent help needed! I really want to save this fish.
Thanks to anyone who can offer suggestions.