Since we had our pool opened a month ago, our PSI has been reading around 26 consistently. Backwashing for 3 minutes a time does not change the reading. The water in the sight glass is definitely clear at the end of backwash. I thought it was the gauge which we replaced yesterday, but the new one shows the same reading and the gaue does go to 0 when the pump is off. The sand in the filter was replaced last summer. Any ideas?