Ben,

Looking at the 1-HP Whisperflo curve https://www.pentairpartners.com/prod...ctcatalog.aspx I'm trying to figure out what my pump is really pushing.

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?

Looking at the chart on pg. 157 and going by the curve represented by "G", which is shown to be the 1-HP whisper-flo (1.65 service factor) it's showing that I should have about 90 GPM of flow.

Taking the low speed chart "B" and considering that I have about 6 psi of backpressure on the system = 13 ft of head. "B" shows at least 40-50 GPM at ~13 ft of head.

Of course I'm not counting head losses from the 2-3 ft of head losses on the suction side so it would be a little bit lower. Also consider that my return piping is 1.5" from the filter to the pool. 90 GPM is way more than the filter is designed for so that would definitely explain why it has never filtered very good.