Go to Tractor Supply or Attwood's and buy a stock tank heater for $30.00 or less. We had single digit temps for several days and the ices was 3-4" thick on my tanks. I put a new heater in one of the tanks overnight and the ice cap was gone the next day. I just kept rotating the heater to the various tanks to keep the tanks open. The aerators also kept the water moving to reduce the ice too. My tanks are 100 gals and 300 gals. These are used to keep the horse and cattle water troughs open thru the winter. Works like a charm. I have used them for 20 years.