Agree with Limpid for the most part. QT should be used for one fish at a time for most situations. Exceptions would be when you get multiple schooling fish (3 chromis, for instance, that sort of thing) or a couple clowns from the same source tank in your LFS. Never ever add another fish to a QT if there's something already in there....at best it "resets" the qt clock for the first animal, and at worst you can give the older animal a pest from the new addition.
I'm sorry to hear about the lemonpeel. Sounds like it was a shock issue from transport or possibly acclimation to or from your LFS.