hmm.... i never even thought about that.... our power was off for a week this winter with the ice storms, I had to pull everyone out and shove them into my inlaws 29 gal tank.... that was fun!.... but when the electricity came back on and the temp got back up to normal from 35 deg., I just did a water change and put them all back in. I only lost 3 fish and that was it just got too cold for them before I could get them out.