If you have a heated tank, forgive me but I read a bunch of threads every day and forgot who's got what. I would take some water out and float aged new water in cups on the surface until the temp is acclimated and then just pour the water in. If your working with room temp water (like me) make up a gallon of water with chemicals and let it sit for a day to get room temp. Then siphon out about half of the water in his tank and slowly pour the new stuff it. Tada 50% water change :) Thats how I do it at least.