Correct me if I am wrong, but as far as I know, there is no way to 100% rid your tank of ick. That's what has always been told to me. Now, fish like a Hippo Tang are very sketchy/stressful fish to begin with and that is reason they are usually the first fish to show signs of Ick. But the reason it got ick is usually because something in the water is out of wack and causing unneeded stress on the fish.