You're describing "ich" quarantine - then there are wrasses (must be treated for internal parasites), then there are corals should be trated for flatworms, redbugs, nudis, etc...
if you have no QT - try to use someone elses, and if you still don't have any - watch in the sellers tank as long as you can...
I'll sound like a jerk, but the answer is, IMO, get one and be VERY careful about what you bring in until you do. Preferably, bring in nothing until you do. Really, a decent QT setup won't cost you more than about $50 if you buy it all brand new.
