I agree with Bryce. I refill my tank after a water change with cool water. It is probably in the high 60'sF, and the fish seem to love it. Once, I tried to add warm water with cold water via buckets (remember those days?); the water was too warm and I had some issues with fish being stressed for a day or two. Adding all cold water has never posed much of a problem, but if the tank temp. drops too much, I feel a bit uncomfy personally. So, cool water via Python is the way to go.