Hi, can anyone advise me on what size pump to buy. I have a 15' round 3.5 foot pool. It has a Hayward Hi Rate sand filter 100lb. model S166T. I was told I need a 1 hp pump. Is this correct or can I get away with a smaller one? I called Hayward and they recommended the Power Flo Lx. My motor is good. Thanks, Carolyn