We opened our pool this year and everything was going fine. We cleaned the DE filter, put in the DE and the pressure was fine. However, after 1.5 hours, the pressure was gone. We primed the filter and then the pressure is good again. But then, it loses pressure again. Can anyone tell me what is going on? We've had our pool and filter going on 8 years. This has never happened before. We did backwash because we had a lot of algae. We put in more DE and at first, its fine, then no pressure. How often does these filters need to be replaced? Is it time for a new one? We got a new pump two years ago.

Many thanks.