Yes, for at least 4 weeks.
If signs of illness shows up it will be longer till the signs are gone and ad three weeks to it.
If you have fish in QT for three weeks and ad a new fish the QT start back over again.
I treat all new fish with Prazi-pro. Otherwise, just monitor and get them eating well from there. If they show signs of other diseases, I treat from there as needed. Things to watch out for include Ich, velvet, parasites, etc. Before a fish should be moved from QT it should not show any signs of disease, and it should be eating all of your prepared foods (there may be one or two an individual fish doesn't care for, but as long as it eats everything else, you are fine).