First, you never want to use medication in a QT unless you suspect the fish has something, then, if it does, treat with the correct medication.
As for ammonia, you're always going to have some, even if you run some type of biological filtration you're probably going to register some ammonia. What you want to do with make sure you don't overfeed, actually feed very lightly, and vacuum up any uneaten food. Don't worry too much about the ammonia, just do large water changes
weekly and watch the fish. If you see them acting funny then do a water change. Basically after the first week you can actually do a completely water change, including cleaning out the QT completely.
Also how large is the QT?