Having an issue since opening my pool a few weeks ago. When on recirculate the pool has really good pressure and maintains prime however when in filter the return jet looses pressure within a few hours and the pressure gauge on the filter will rise 10psi and the skimmer basket looses its prime. The filter grids are glean and only a year old I have a brand new motor and multiport valve. I don't see an air leak anywhere. it's a Hayward de filter. I'm getting pretty frustrated since I can't seem to find the issue. Any help would be much appreciated.