For the last couple of years, I've taken more time to acclimatise any new additions. When the assistant has bagged the fish, I ask for an extra bag of the tank water. I put the contents of both bags into a bucket when I get home, then add a cup of tank water to the bucket every ten minutes or so. It usually takes well over an hour, but it's worth it to me. I just think it's best to acclimatise any fish slowly.