I have only bought fish 3 times, the first batch of goldfish, the first batch of koi, and the second batch of koi. I didn't quarrantine at all, but now with my mystery fish deaths I think I need to do it, but I don't really understand. If I keep new fish seperate, and they dont' die after what 2 weeks, then it's safe to put them in with my other fish? What if it's not something that kills all fish? What if it's just something that the new fish are immune to, they could still wipe out all of the other fish evne after a month. What is the process for quarrantining? Am I missing something?