how big of a sand filter do i need
If you don't already know how many gallons are in your pool, consult the pool's manual or manufacturer. Check out the size of your pump. The pump size will vary between 0.75 and 2.5 hp; the size is indicated on the side label or in the manual. Use the pool gallons and pump size to choose the right sand filter size. A 3-square-foot sand filter is used for pools with 10,000 to 15,000 gallons of water with pump sizes of 0.75 to 1 hp. A 3.9-square-foot sand filter is used for pools with 20,000 to 25,000 gallons of water and a 1.5-hp pump.