Hi, bought a home last November with a 15 by 35 fiberglass 22,500 gallon pool. Found TFP for advice on water chemistry and have a sparkling clear pool. Problem I'm having is with the pump sucking air. There's been a few times basket runs full but most of the time it's not. I've looked all around lid and basket housing for leaks or cracks when I shut pump off and can't find anything. It's a 1 hp motor and sta-rite 240 sand filter. Impeller is clean. Any advice? Thanks