Ick as I have asked before, will appear even after QT. So in all honesty it is something that is a normal parasite in an aquarium. If you feed your fish normally and make sure they are healthy, they will beat it on their own. If it already has ick and you quarantine it, the ick is already in your DT. So even after it beat the ick in QT, when you put it back in your DT. It is eventually going to get it again. I would definitely QT for other types of disease, but I wouldn't do it for Ick. Just my personal opinion.