I have never had a quarantine tank, not because it isn't a good idea to have one, but because I almost always completely stock my tank within a month when I set it up. I also don't do "cycling". I heavily plant the tank, start fertilizing, wait a week or two, then add a few fish, wait a week and add a few more, wait a week and add the rest of them. That has always worked well for me. But, no question, if you pay a lot for your fish, and I don't, you should quarantine new fish before giving them a chance to infect your investment.