Mas985, I have a real long thread over at the balancing water forum. I bought the pump new off eBay and got sand filter on Craigslist. Sand filter is a Hayward s200. I run 17 psi on filter, recirculate. And 10 on backwash. Psi never goes up. Started with algae, killed it but best guess is pump pushed dead algae through filter to fast to filter it out. Got a cloudy mess now. Watermom and Ben has been giving great advise. In short though the return flow to the pool is very powerful so I'm looking to slow it with smaller impeller or a shut off valve between pump and filter and close it enough to slow the flow. I saw impellers for this pump down to 3/4 but maybe 1 hp would help