I agree with Frogspawn.. but i still don't follow the guidelines lol. I've never QT'd anything before.. ever and i've never had a problem. But that could be because i either got lucky.. or haven't had the tank long enough to experience a problem haha. Either way.. if you have the money, definitely QT. It will save you money in the end if fish/stock ever get sick, rather than just letting the animal just die.