Article - Pumps and Filters in Winter
Pumps and Filter Care in Winter
You won’t need to filter the water but it’s a good idea to keep it moving at the pond’s surface.
Pond life needs oxygen even during hibernation. If ice covers the surface of the pond, oxygen can’t get in and toxic gasses can’t get out.
Submerged pumps with fountains or waterfalls will oxygenate the water and keep a portion of the pond from freezing. If you live in an area that freezes solid I recommend using a pump and fountain to aerate the water.
Set the pump on bricks about one foot below the water. This will prevent the pump from getting clogged with leaves.
If your fountain output appears to be diminishing, check the pump to make sure it is not clogged. Floating pond heaters are available to keep a small area free of ice.
You can also use an aquarium air pump and diffuser stone to oxygenate and prevent ice formation. Even if the pond completely freezes over, the air pump keeps pumping oxygen into the water.