quarantine v. FW dip

Question
Was wondering..is it worth stressing a new fish with a FW dip prior to adding it to the tank? I dont have the room for a QT in my apartment and my first fish (false perc. clown) ended up having a parasite..i think.  A week in he developed a white spot on his pelvic fin and kept it retracted. (thought he was missing a fin!) A FW dip fixed the problem for a few hours but the same thing happened all over again. Please advise if you can, Thanks!

Answer
i personally have never done a FW dip on my fish, i just try and make sure they all look healthy in the shop before i buy them. If by chance they do get sick i make sure they get lots of food, this boosts their immune system ans enables the fish to fight it off themselves.