I hope you dont' add the water from the fish store bag into your tank? You should just net the fish and add just the fish to the tank. Fish store water may contain pathogens.That is not a stupid question! It’s something I never thought about. I float the bags containing new fish in the tank for 15 minutes or so & release them. I make regular water changes, nothing special. The volume of pet shop water is very low compared to the tank water.