FWIW, today I checked the Vertex system that I installed a month ago. 3/4 hp compressor, 3 dual air stations. 7' deep is on a roughly 80' run, 5' deep one is on a 100' run, 4' deep one is on a 175' run. On initial start-up the gauge showed 0 back pressure. Today it was showing 3 psi backpressure. Shutting off the deepest diffuser bumped the backpressure to 6 psi. (quick off and then back on for a test) The deepest diffuser has the valve opened all the way, the 5' diffuser has it opened about 75% and the 4' deep diffuser (even tho it's the longest run) has the valve open slightly more than half. The valves are set like that to even out the bubble boil between the 3 diffusers.

Airline is all self-weighted. 1/2" or 5/8" I.D., I forget which.

Thanks again Sue!! wink

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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).