what I usually do when I buy tang.
Put them in qt where you can take them out easily, look at them every day, if you see ick started to outbreak, fresh water dip for at least 5 miniutes every day until you don't see any more, just leave them in qt for 2 weeks before you put them in the show tank.(don't use any chemicals before you try this treatment incase you have a servere problem). I hope this will help.