Well, when we had a ice storm during the winter, the power was off for awhile, I used a battery operated airstone and wrapped my tank with blankets, to try to keep the heat in it. But thats all I could do. I also have a generator, but my parents wouldn't let me leave it running in my room (where my tanks are), being so loud lol. I guess if it's hot outside and you lose power, you can use ice? to keep the tank cool, since you won't have any cool air on in the house