Hayward Sand Filter Issues - Help Please
I purchased a foreclosed house this year with a basic in-ground concrete pool. Although the filter system seemed to work OK at first, it has lost efficiency and now spews dirty water back into the pool through the returns whenever I vacuum. After trying multiple backwashings, I have now replaced the sand with the correct amount, checked the filter laterals, and replaced the slide valve O-rings, but it still doesn't filter well and still returns dirty water to the pool when vacuuming. The filter pressure has always seemed low (~8 psi), but after replacing the sand it is now at only 3 psi. Water flow seems good when I backwash, so I don't suspect suction issues. Pool specifics include: ~19,000 gallon volume, Hayward S244 sand filter, Hayward two position slide valve, one combined 1-1/2 inch suction pipe from the skimmer and main drain, two 1-1/2 inch return pipes to the pool. Any ideas as to what's wrong?
Thanks in advance for any help!