Residential pools run one of three filter types: sand, cartridge, or DE (diatomaceous earth). All three do the same job, but they trap debris differently, need different maintenance, and fail in different ways. Knowing which one your pool has tells you what kind of care it actually needs.
How to tell which one you have
A sand filter is a large tank, usually with a multiport valve on top or on the side, with settings like Filter, Backwash, and Rinse. A cartridge filter is a tall tank that opens up to a pleated cartridge you can lift out. A DE filter looks similar to a sand filter from the outside but holds a set of grids coated with fine white DE powder.
Sand filters
Water pushes down through a bed of sand that traps debris. When the pressure gauge climbs well above its clean baseline, the filter is backwashed to flush the trapped dirt out. The sand itself lasts a long time, but over the years it can channel or harden, and a cracked lateral inside the tank sends sand back into the pool.
Cartridge filters
Water passes through a pleated cartridge that catches debris in its folds. There is no backwashing: the cartridge comes out and gets rinsed, and eventually replaced when the pleats wear thin. A torn cartridge shows up as debris returning to the pool no matter how often you rinse it.
DE filters
DE filters polish water the finest of the three. Grids inside the tank hold a coating of DE powder that traps particles sand and cartridges miss. They are backwashed like sand filters, then recharged with fresh powder, and torn grids show up as a puff of white powder blowing back into the pool.
When it stops being maintenance and becomes a repair
Some symptoms point past routine cleaning: pressure that spikes again right after a cleaning, water that stays cloudy with the chemistry balanced, sand or DE powder appearing in the pool. Those usually mean something inside the tank is damaged. Our pool equipment repair covers filters on all major brands, and our weekly pool cleaning includes a filter inspection on every visit, so problems get flagged before they grow. Request a free estimate if your filter is showing any of these signs.