I'll be devils advocate here since I agree as long as they are done properly. However I believe QT kills a lot of fish. How? They are thrown together quickly in panic, not cycled or ran properly and people don't realize meds can kill of some of this good denitrifying bacteria. There is not as much surface area for denitrifying bacteria, they are smaller than DT and rarely do I see them properly cycled. So ammonia is #1 killer in QT tanks. Not near as natural of an environment so they stress and barely eat. Just save the expense and buy from ERC. Even if the tank is already infected at least the fish is parasite free for the most stressful part (the first few days) and if they do contract the disease by the time it's full blown their immune is able to fight it off.