Pond aeration sizing calculator

These figures come from vendor rules of thumb, so treat them as a starting point for a design. A deep, narrow pond or one with coves needs diffusers placed basin by basin. Run the system continuously in summer, and after any long stop follow the staged start-up so the pond does not turn over and kill the fish.

A bottom diffuser works by lifting a column of water from the bottom to the surface, where it picks up oxygen. The bubbles themselves add little. That column needs depth to work in, so under about 8 feet a surface aerator or fountain does more (the small pond aeration calculator). The compressor is the smallest in the Kasco and Vertex ranges that delivers the CFM. A 1/4 hp unit gives about 1.6 CFM, a 1/2 hp about 3.3, a 3/4 hp about 5, and 1, 1.5 and 2 hp about 6.5, 9 and 12.

The staged start-up matters most in summer. A stratified pond holds cold, oxygen-free water below the thermocline, and turning it over all at once mixes that water through the whole pond and can kill every fish in it. Doubling the run time each day lets the pond mix gradually. Follow the same schedule after any stop of more than a few days in warm weather.

Sources: Kasco Marine and Vertex Water Features diffused aeration sizing guides. Practitioner discussion: Pond Boss forum thread Aeration simplified.