Yeah, I never trust anyone to QT but myself. You really only have those 2 options - leave them in the DT or catch all the fish, put them in QT (best to use the tank transfer method - but that requires 2 sets of hospital tank equipment), then leave the DT fallow for 72 days. You have to weigh the pros and cons of catching all the fish, stressing them out, then having to maintain them in QT for 72 days, but having the pro of knowing you eradicated your system of ich. If you leave them in the DT, you can hope that the ich doesn't spread and hope that through diet and good husbandry, the ich will lay dormant...until you add more livestock or stress them out...