Ballpark figure go with .5 psi for every foot of diffuser depth. Also, look at the volume of air that you are pumping vs. length of run for that particular size tubing. Smaller dia has more friction. Like trying to breathe thru a straw vs. a 1 1/4" piece of tubing.

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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).