De-icers form a hole in the ice allowing nasty gases to go out and clean oxygen to come in. If your pond allows it you can leave your waterfall running to keep a hole in the ice or form some beautiful frozen falls (though we recommend having a de-icer).
“But if I have a hole in the ice why do I need an aerator?” Frank thinks to himself.
You’ll also want an aerator about 1 foot below the water’s surface. Aerators add oxygen to the water and move it around so it doesn’t stagnate. During winter, your fish hibernate in the warm water at the bottom. Keeping an aerator near the bottom during winter will mix the warm water with the cold which will make your fish cold and uncomfortable.
If you have an Ion-Gen we recommend turning that off as well.