Pond aeration sizing calculator
These are vendor rules of thumb, not a design. A deep narrow pond or one with coves needs diffusers placed per basin. Run continuously in summer, and follow the staged start-up after any long stop to avoid a turnover kill.
Method and sources
compressor CFM = 1 per acre, minimum 1.5
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 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 in summer. A stratified pond holds cold, oxygen-free water below the thermocline; 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.