With that 18' water depth, you are better off going with the rocking piston. As much as I like the rotary vane compressors, the vane life is shortened when pumping air at the upper end of their design parameters. I have a customer that rebuilds his 3/4 Gast rotary vane compressor yearly because he's pushing air down to 20' water depth.

For summer aeration, use the diffusers that produce the finest bubbles available. You will move more water to the surface that way. For shallow water winter aeration (or it could be called ice prevention) use the coarsest bubbles possible with as much CFM as you can to create the most waves.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).