When I did my routine weekly water change on my tanks last week, I dicovered that the heater in my 10-gal fry tank had been disconnected for a week. The water was chilling cold when I touched it and when I read the thermometer, the temperature was at 67F. I normally maintain the temperature at 76F. I have around 50 1-month old leulupi fry and a couple 1-inch bristle nose pleco in the tank. Surprisingly, I haven't lost a single fish and there was no outbreak of ich. They continued to eat during the week that I have forgotten to connect the heater. The only sign I saw was that the algae was on the glass because, apparently, the pleco did not eat. So the fish must be quite hardy and can tolerate days below normal temperature.