My presure at when I just pre-coated the filter is 12. Are you saying that 12 x 2.31 = 27.72 is my head? That seems really low.

I have a 20x40 pool with 3 home run suction lines (2 skimmers, 1 main drain) of 2 inch pipe....and 2 1 1/2 inch lines for returns with 2 jets on each line (total jets 4).

Filter is a 1 hp Northstar

Using that calculation....I'm pumping some MAJOR gpms.....that sound right?