I did some looking around and found this page:
Scroll to the bottom and it will tell you how long you should continue treatment of the product.
, I have no idea how accurate that information is. It looks professionally done and has a lot of info there so it is probably fine. Just wanted to let you know.
Oh, one more thing. You will need to keep that fish in quarantine at least 4 weeks from the time ich disappears from the body of the fish. Remember, just because you can't see ich on the body of the fish doesn't mean you have eradicated it from the system. It probably just means that it is in another stage of its cycle.