WHAT!!!! How? I have them floating in their plastic bag in the pond right now. QT them for 4 week where?
With new fish, they could carry disease and make your other fish sick. People recommend quaratine new fish in a seperate holding tank for at least 4-8 weeks since some disease you wont see them until a long time. The new fish usually stress out to the max already being caught and transfer, so they are easy to get sick.
I have to admit that I can only do it for a few weeks, and haven't done so with the last group. I risked my older fish there. I gave my new fish a salt bath though just to kill off any parasite at least. I try not to get new fish just because I dont have patient or space for quarantine. But when I do, I put it in my indoor tank (pretty tight space so I dont want to do it often.)