Had to put a 2nd tank heater two days ago. One 1500 W would not cut it. High today so far is 8 degrees, looking at -6 Sunday night.
Lack of water is the most significant cause of colic in equines in the winter
I have a retired 15 cu ft chest freezer as my water tank. There is a hole in the lid to drink through. Its pretty beat up and plan to build a new on this summer.
I have a sinking 1500W heater in it. Never have had ice in it (if the heater was plugged in). Gotta think it doesn't cycle all that much.