Just from my experience. Like you said all the parameters are ok in the main tank, then there should be no problems taking water from the main into the hosp/QT. Just add a filter, heater (if necessary), and some hiding spots. I used cheap "fake rock" not uncured just fake) or pvc piping. The tank should be the same as your main, but just make sure (ease of mind). I also, before I knew better, added a thin layer of LS, but you should paint the bottom to help with reflections and aggressiveness towards themselves. Yes, get all the fish out, and start hypo from there. HTH