I QT all new fish I buy online or from the LFS's. I did add my Sargassum Trigger straight to the DT, but he came from a local reefer's 7-footer with 5 tangs, all of which were long established and in great shape, so I had no qualms. There are plenty of reasons besides disease to QT fish, esp. more 'expert' fish where getting them to eat is important, as otherwise in a packed display, they wouldn't stand a chance.