Need some help trying to figure out issue with pump. It was working great and had no issue priming with a really strong return. Now the pump won't prime, but the return is still really strong with a lot of air bubbles coming out of the return with the strong current. The water level doesn't seem low but adding water anyway just incase, but still not priming even after more water has been added. I tried backwashing and tried turning pump off and then on again.