I have a Hayward sand filter with 350lbs of sand. I bought the cheap stuff from Home Depot (Quick Crete). My pool is constantly cloudy even though chemicals levels test out. After the pump has been running for just a few days, the pressure will rise from 18 psi to 20 psi and basically shut down water flow to a trickle. When I back flush there is rarely any debris in the sight glass, then the pool will drop back to 18 psi and run normally fora few days and the cycle repeats. Is this a sign of bad sand? The bag said it was pool sand, but I am thinking that is my issue. Thanks for your help.