When you get new fish, ask for an extra bag of water. If you have any Protozin, take it with you and add a couple of drops to the bag before its tied up. When you get home (always as quickly as possible, of course) put the fish and the water from the two bags into the bucket you use for water changes. Put another couple of drops of Protozin in the bucket (if you don't have a Q tank, this is the next best thing you can do). Add a cup of tank water to the bucket every ten minutes or so, but do this for a good hour - the longer you can take to acclimatise the new fish to your tank water the better. When the bucket is getting towards being full, then you can pour the contents slowly into the tank. I started doing this around eighteen months ago and have never lost a new fish since. May just be coincidence, but the longer you take, the better.