QT or not QT

[hapki88]

Through my research on setting up a new saltwater aquarium I came across the subject of setting up a QT for all new or sick livestock. This was an eye opener to me since no one had mentioned this before in all my conversations with aquarium owners. So, my question, is it really necessary to have a working QT on stand-by with bio filter, heater, etc. for all new livestock? I've read you should QT a new fish for 6 weeks before placing him in the main tank.

Thanks for your help.