Sand filters, which are a bit more expensive than cartridge filters, work by passing the dirty pool water through a sand filtration system. The dirt particles are caught in the sand and the clean water is sent back to the pool. They are usually more expensive than cartridge filters, but also just as easy to maintain.
When the sand gets dirty you must perform a backwash, running the filter in reverse to remove the excess dirt (there is a backwash spigot so the dirty water doesn’t return the pool). Unlike a cartridge, you can use the same sand for approximately five years.