Big head scratch-er. So today, flow reduced. Tried something new. Just shut off pump and turned right back on. The Pump has a "Priming" start speed of 3450 RPMS. It stays at this level until it senses good flow (primed) or 10 secs. Just shut off and turned on a flow returned. Also, in the afternoon as the flow reduced, I through the Valve into recirculate. Stayed stings rest of day. Switched back to filter and flow was good (no backwash). Tomorrow I am going to soak in TSP for a few hours. Has to be in the filter and just maybe the Phosphate free TSP didn't clean it good enough
Will report back tomorrow.
Really can't be the filter unless you also have a bad pressure gauge. Any clogging or restriction in the filter would show as increased pressure.