Quote Originally Posted by TheGoose View Post
Taking the fact that I have 20 psi of backpressure, and 1 psi = 2.31 ft of head, then is it safe to assume that I have 46.2 ft of head, or to make it even about 50 ft of total head?
You have to add 3' for the height of the filter gauge above the pump and as you pointed out, there is suction head as well but with 2 suction lines, it should be fairly small so I agree that the flow rate should be at most 90 GPM. Also, low speed is simply half the flow rate of high speed so you really don't need to use the low speed head curve.