i lost half a tank of fish because i didn't think it was ich, thus i didn't QT
that one fish. i just observed. the thing with observation on this matter is that: what are you observing? when the symptons are visible it's usually too late.
all your new additions.
my situation was almost identical as yours: new tanks, clownfish, etc. the maturer your tank becomes, the less likely it'll happen.
you cannot be too careful.
don't get carried away by the garlic remedy either. i tried it and it didn't work. it made the fish eat more but at the same time polluted the water. a new tank already has unstable water conditions to begin with, do you want to make more changes to it?
bottomline is, take all our advices with a grain of salt. every single tank is different. there's no one solutions to all.