We live in Georgia and are having below freezing temperatures all week. Should have turned off the waterfall; it froze over last night and drained water out of pond. Besides leaving waterfall off, and pump running, should I purchase a heater for the pond? I have a small electric heater that only keeps a hole in the ice, when the top of the pond freezes. Luckily, was able to add water back to pond; not sure if fish made it, still dark outside.