Quote Originally Posted by Sumo1 View Post
I would think that drawing water from more sources than just the main drain would have lowered FP.? TIA
When you close the skimmer, you are restricting the amount of water the pump can take in, so you are limiting how much it can pump. Pressure is measured on the outlet side of the pump, and is an indication of how hard the pump is working to force water through the filter and return plumbing. The less water the pump is trying to push, the easier it is to get that water through the system, so the pressure will be lower.