Agree. I've learned the hard way as well. I've had two major ich outbreaks due to not quarantining, and I hope I never have any more. Both times were from introducing new rummy nose tetras. The first time, I got some delivered and put them straight into the tank. The same day, I noticed that they were all covered with ich, but I didn't have a qt tank, so I just got meds and treated the tank. I lost most of the rummy's, and all of my fish got it, except for my breeding pair of discus, amazingly. Then last year, I got some more rummy's from my lfs, and they looked fine so I though it will be okay this one time... Well, nope, and they got ich and spread it to everyone in the tank. This one was even more stressful because it was like a tera massacre and they were dying by the hour, and I lost the beautiful female from a breeding pair of angel fish, which was seriously a horrible death to watch. She seemed like maybe she was going to start pulling through but over the course of a day, she lost all colour and started whirling around the tank, upside-down in the current until she died. Bottom line is a now have a smaller qt tank, and keep the filter cartridge in my external.