I got this pool with the house and it has a hayward sand filter. I replaced all the sand and inspected the laterals and everything was in ship shape. 300 pounds of new sand. It seems to work properly and filter fine, but the gauge shows 2 PSI after a backwash. If I add DE i can get the pressure to about 3 or 4, then usually 4 or 5 days after adding DE the pressure creeps up to about 10 then I backwash it and start over. Is that normal for the pressure that low? Pool has 1 skimmer and 3 returns. Should I plug one of the returns? Its in a weird spot below the skimmer and to the right, about 18" lower than the two returns in the corners.