Your aerator doesn't make oxygen. It moves water.
Your aerator doesn't make oxygen. No machine in your pond does.
The oxygen your fish breathe comes from the air above the pond and from the plants in it. (1) The air's share only gets in where air touches water, and slowly. (3) Your aerator's job is to make that surface work harder.
The night shift
Plants make oxygen only while the sun is up. After dark, everything in the pond keeps breathing: fish, plants, and the bacteria breaking down leaves on the bottom. In midsummer, oxygen falls all night and bottoms out just before sunrise. (1) Warm water also holds less oxygen than cool water to begin with. (1)
The layer problem
On a calm, hot day, the top of a pond warms fast and stops mixing with the cold water underneath. The bottom can run nearly out of oxygen, and when it does, the muck releases phosphorus that feeds algae. (1)
What the bubbles do
An air pump on land sends air to a diffuser on the pond floor. The rising bubbles release oxygen and set up a current toward the surface. (3) Penn State says this spreads oxygen through the pond's whole depth and can cut the phosphorus that feeds algae. (1)
Winter turns it around
Once ice seals the pond, no oxygen comes in from the air. (1) Snow on the ice cuts the light, so plants make less oxygen. (2) Penn State Extension calls this winterkill: fish lost in winter because oxygen is lacking. (2)
A de-icer holds one hole open in the ice so toxic gases can escape, and most owners won't need a separate pond heater. (7) Paired with an aerator, the moving water helps push those gases out. (7)
In winter, the air goes shallow. Water is most dense at about 39°F, so the bottom of a frozen pond stays slightly warmer. Scott Jones, an Extension specialist at the University of Arkansas at Pine Bluff, suggests winter diffusers at a quarter to half of the pond's deepest point. (8)
Not sure what yours is doing?
Some ponds have an aerator, some a de-icer, some both. If you're not sure what's running in yours or whether it's set for winter, give us a call at 720-248-2471.
Sources
Each page was opened and read on 4 November 2026.
- Penn State Extension, Dissolved Oxygen Basics for Pond Owners. extension.psu.edu/dissolved-oxygen-basics-for-pond-owners
- Penn State Extension, Winterkill in Ponds. extension.psu.edu/winterkill-in-ponds
- University of Arkansas at Pine Bluff, Aquaculture and Fisheries, Pond Management: Aeration. uapb.edu/?p=4426
- U.S. Environmental Protection Agency, Indicators: Dissolved Oxygen. epa.gov/national-aquatic-resource-surveys/indicators-dissolved-oxygen
- U.S. Geological Survey, Water Science School: Dissolved Oxygen and Water. usgs.gov/water-science-school/science/dissolved-oxygen-and-water
- Penn State Extension, Common Causes of Fish Kills in Ponds. extension.psu.edu/common-causes-of-fish-kills-in-ponds
- The Pond Guy (pond-industry supplier), How to Size a Pond De-Icer. thepondguy.com/learning-center/size-a-pond-deicer
- Scott Jones, Extension small impoundment specialist, University of Arkansas at Pine Bluff, in "To aerate or not to aerate winter ponds." pbcommercial.com/to-aerate-or-not-to-aerate-winter-ponds
