Aeration moves air into the water and keeps it circulating, which helps maintain dissolved oxygen for fish and beneficial bacteria. Small and mid-size ponds usually use an air pump with one or more diffusers; larger ponds and lakes use cabinet compressors with weighted tubing and bottom diffusers, or floating fountains that add surface movement and a display.

Size an aeration system by surface area and depth, not just gallons. Deep water needs a compressor rated for the pressure at that depth. Questions on sizing? Call Mystic Koi & Water Gardens in Upland, CA at (909) 920-3767 and talk to people who build and keep ponds every day.