I can speak to this... so, hubby and I went to see his family in Idaho (before we moved here) for Thanksgiving. Hubby turned the heater off in the apartment (its winter mind you) while we were away... we returned, 4 days later, tank temp. was at 62 degrees.... now while no one died, everyone looked like ****. All fish (included clowns) were dead white, moving slowly, fins were even shredded a bit on my royal pleco (at first I thought he was dead) - I dont think they would have lasted much longer.... turned the heat on, slowly brought temp back up and all was well but - things were not looking good... moral of the story - I wouldnt "try" it