We installed a new 20x54 ultra frame by Intex. It came with a pump and sand filter. When we first set up about 4 weeks ago the psi was almost to the yellow on the gauge. Yesterday afternoon it dropped to about 2 psi. I back washed and rinsed. But today it is still at 2 psi. I did notice that the flow from the return seemed less turbulent than before. Is something wrong with the sand filter or the pump? I am thinking it is sucking air somewhere and not building up the pressure?