To be honest, if I buy fish from a pet store, I put them in my aquarium and try to minimize the amount of pet store water that enters my tank. I just put the fish in their water bowl when I'm ready. Then I clean the water bowl and change the water. To be completely honest, sometimes I even trap wild fish and feed them to my snakes. It would be irresponsible for me to recommend doing that, but it's the truth. I also know that it increases the risk of transferring parasites that have to be dealt with before brumation.

Rick