Yeah, 10-12 weeks with 12 being the preferred is what I've read. Keep those copper levels steady with the water changes and you should have it under control.
My Hippo Tang gets Ich still in my tank, everytime I stir it up a bit, or re-arrange the rocks. She's the only one, gets it for about a month or so, and it goes away by itself. She always remains active and eats.