Earlier this summer the pump was ran dry for about 20 minutes b4 I caught it and it has been working, but not like it used to. It's never built up the same pressure since, even with a new filter in it. 2hp hayward and hayward cartridge filter and our pool is 18' x 54" abv grd. I have a friend who recently took his pool down and has been sitting on his system that is a 1hp hayward power flo st1580z2lx and a 18" hayward sand filter. He wants $150 for it. It seems like a good deal and I think my 2hp is too much pump for the pool anyway and isn't a sand filter a better filter than cartridge? So TFP community, my question is, should I buy it?