I don't know anything about buying filters. I have sand so I know I want a sand filter. I am probably going to get a 1 horsepower pump, but the rest I'm not sure about. How important is the "gpm" as well as the size of the filter, the amount of sand it can hold. There are a couple on craigslist I'm thinking about. One is a hayward S166T. It only holds 100lbs of sand and is 35 gpm. The other filter I haven't gotten specs on yet. Please help I'm clueless. and I desperatly want to clear my green pool!