I have a hose connection tee'd inbetween my hot and cold water with valves to adjust each to the proper temperature. You have to be careful though, other things in the house using water can affect the temp. and you have to becareful about absorbed bubbles. When filling with heated water the water can create a high level of absorbed bubbles which will attach to your fish's gills and suffocate them. The way to get around this is to fill slowly, and watch the outlet of the hose.