Sand filters are better for most pools.

Cartridge filters are fine for small above-ground pools or if you really hate backwashing. But for a typical in-ground pool, a sand filter is cheaper, simpler, and lasts longer.

Sand filters work by trapping dirt in a bed of sand. When it gets dirty, you backwash—reverse the flow and flush the gunk out. That’s it. A bag of pool-grade sand costs like $15 and lasts five years. No cartridges to replace, no cleaning with a hose.

Cartridge filters use a pleated paper-like element. They filter finer particles than sand, so your water might be a little clearer. But you have to pull the cartridge out and spray it down every few weeks, and replace it every season or two. Those cartridges aren’t cheap.

If you’ve got a tiny pump or a spa, go cartridge—it takes up less space. For a real pool, get the sand filter.

Future you will appreciate never having to scrub algae slime off a folded piece of paper.