Ok so I back washed the filter which lowered the psi from around 20 to 15. I put the filter on recirculate and closed each the drain and skimmer valves separately. When I closed the skimmer valve (water being pulled from main drain only), it seemed to be having trouble getting water to the pump. The pump seemed to pulsate as if not getting enough water and the pressure gauge on the filter would go up and down with the pulsating (0 to 10 back to 0 to 10 and so on). To me this seems like there is blockage in the pipe. When I closed the other valve everything seemed smooth and it was getting more water. Any suggestions?