When we moved, my lionfish, 2 hermits and 2 snails were put in a 20g for 2 days while waiting for the 90g to be delivered. The 20g had the filter from his original tank, rocks, heater, shells, etc....On the first night the tank was left alone at the new place and the central heat was turned on. Wouldn't you know that the heater in the tank and the central heat thermostat both failed that night? When I got there the next day, the water temp was 65 degrees. Took hours to bring the temp back up to 80 because I didn't want to stress him and the others out. Everything ended up surviving this, but if I ever move again, I will never leave a newly set up tank alone like that again!