I show how I make a insulated cover for my stock tank by recycling an old exterior door. I then show the difference the cover makes keeping my stock tank ice free with my small 500 watt deicer. If you don't have access to a free scrap door you could use a piece of plywood and some insulation. The cover does a few things; first it limits evaporation, second it traps the heat, 3 it stops the wind from removing heat/cooling the water. This means you can use a smaller heater or depending on your climate no heater to keep your tank ice free, also you don't have to fill the tank with water as much.