24-inch vs 30-inch sand filter: 24-inch is the standard for 20k-gallon pools

A 24-inch filter handles flow and turnover fine for a 20,000-gallon pool. A 30-inch gives slightly longer cycles between backwashes and more tolerance for heavy use, but it’s not necessary. The real mistake is going too small—a 20-inch filter means constant backwashing and wasted electricity.