Help. We had a hayward sand filter it ran for 30 minutes then slowed down, so we were told to check the impeller (it was clear) change the sand which we did.. Ran the pump and filter all good for 30 minutes then again slow. So we purchased a brand new hayward DE filter and pump, and all new hoses. Ran it for 30 minutes then again it slowed down. Had a pool company come in and vacuum it thought debris maybe the issue. Same thing ran for 30 minutes and slowed down. Does anyone have any ideas. Pool guy added shock and more DE earth and checked water level said all good. he had no idea what could be the issue, said maybe defective pump and filter, we said but same thing happened with the sand filter. thought maybe its the timer and it is slowing down the pump but don't know how to check. Anyone have suggestions.