How to Clean a Pool Filter

When should you clean a pool filter?

Clean the filter when the pressure gauge on top of the tank reads 8 to 10 PSI higher than the pressure you saw with the filter freshly clean. That clean baseline is the number to write down or remember when the filter is brand new or just serviced; on most home filters it sits somewhere around 10 to 20 PSI. As dirt loads up the media, flow drops and pressure rises, and once it is 8 to 10 PSI over baseline the filter is choked enough to hurt circulation.

Pressure is a better signal than the calendar, because how fast a filter dirties depends on swimmer load, pollen, algae, and how much the pump runs. Other tells back it up: weak return jets, a skimmer that barely pulls, or water that stays hazy even with good chemistry. If you do not know your clean baseline, clean the filter once and note the pressure right after; that becomes your reference point.

Do not over-clean either. A filter that is a little dirty actually traps finer particles than a spotless one, so chasing zero never helps. Let the gauge tell you. If pressure rises again within days of a cleaning, the problem is usually in the water (an algae bloom or fine debris), not the filter, and that is worth checking with the cloudy pool guide.

How do you clean a cartridge pool filter?

To clean a cartridge filter, turn off the pump, open the air relief valve on top to release pressure, then remove the lid clamp and lift out the cartridge. Spray it with a garden hose, working top to bottom and angling the water down into each pleat to flush out the trapped dirt. Rotate the cartridge as you go so you reach every fold. A regular hose nozzle is enough; skip a pressure washer, because the high-pressure stream frays the pleat fabric and shortens the cartridge's life.

A hose rinse handles dirt and debris, but it will not remove the body oils, sunscreen, and scale that build up over a season and slowly clog the fabric. For that, do a deep clean every few months: soak the rinsed cartridge in a filter cleaner solution for several hours or overnight, then rinse it again and let it dry. A dedicated pool filter cleaner cuts oils; for hard-water scale, a separate soak works better (covered in the cleaner section below).

The easiest setup is to own a spare cartridge. Swap the clean one in, take the dirty one out to soak and dry at your own pace, and your pump is never down waiting. Pleated cartridges are consumables, so when the pleats are matted flat, cracked, or torn, or pressure climbs fast right after a cleaning, it is time to replace rather than keep washing.

How do you clean a sand pool filter (backwashing)?

You clean a sand filter by backwashing it, which reverses the flow to flush dirt out to waste. Turn off the pump first, then move the multiport valve handle to BACKWASH. Turn the pump back on and run it until the water in the sight glass runs clear, usually about 2 to 3 minutes. Turn the pump off, set the valve to RINSE, run 30 to 60 seconds to resettle the sand bed, then turn off again and return the valve to FILTER.

The one rule that saves expensive repairs: never move the multiport valve while the pump is running. Doing it under pressure tears the internal gasket (the spider gasket) and leads to water bypassing the sand or weeping out the waste line. Always stop the pump before each valve change.

Backwashing sends a few hundred gallons to waste, so top the pool back up afterward and recheck your balance, since you have diluted the water a little. Backwashing alone never gets sand fully clean because oils stay behind, so deep clean the bed once a year with a sand filter cleaner. The sand itself wears smooth and stops grabbing fine particles after 5 to 7 years, at which point it needs replacing; the filter sand and media guide covers what to put back in.

How do you clean a DE pool filter?

A DE (diatomaceous earth) filter is cleaned in two steps: backwash it like a sand filter, then recharge it with fresh DE powder because backwashing strips the old coating off the grids. After the backwash and rinse, with the pump running on FILTER, pour the new DE slurry slowly into the skimmer so it coats the grids. Add the amount printed on your filter's label, since it scales with the filter's square footage; do not guess, because too little leaves grids bare and too much clogs them.

Backwashing keeps a DE filter going through the season, but it does not get the grids truly clean. Once or twice a year, open the tank, lift out the grid assembly, and hose each grid down. If they are greasy or scaled, soak them in a filter cleaner the same way you would a cartridge, then reassemble and recharge with fresh DE.

Never run a DE filter with no DE on the grids. Bare grids let dirt pack directly into the fabric and load up fast, and they wear out sooner. If pressure climbs quickly even right after a fresh recharge, a grid is likely torn and is letting DE blow back into the pool, which shows up as a fine white or tan dust on the floor.

What should you use to clean a pool filter cartridge?

Use a dedicated pool filter cleaner (a degreaser made for the job) or a diluted trisodium phosphate (TSP) solution to break down the oils and organic gunk that a hose cannot. These soak into the fabric, lift the buildup, and rinse out cleanly. For mineral scale and calcium (common in hard water), a separate dilute acid soak works better than a degreaser, since acid dissolves scale while degreasers do not.

Do not use Dawn or any dish soap. Soap foams and is very hard to rinse out of pleated fabric, so the residue comes off in the pool later and you end up chasing foam on the surface, the same way a spa does in the hot tub foaming guide. It is a shortcut that creates a second problem. Vinegar gets suggested a lot too; it can dissolve light scale but it does almost nothing to body oils and sunscreen, so it is not a real substitute for a degreaser.

One safety rule: never mix cleaners. If a cartridge has both oils and scale, degrease first, rinse fully, then do the acid soak as a separate step. Combining an acid with other chemicals can release dangerous fumes. Whatever you use, rinse until the water runs clear and let the cartridge dry before it goes back in.

When should you replace a pool filter instead of cleaning it?

Replace the media (not just clean it) when cleaning stops holding. The clearest sign is pressure that climbs back to the dirty range within days of a thorough cleaning, which means the media can no longer pass enough flow no matter how clean it looks. Cloudy water that will not clear despite balanced chemistry and a freshly serviced filter points the same way.

Each type has a rough lifespan. Cartridges last about 1 to 3 years, sand about 5 to 7 years, and DE grids roughly 5 to 10 years with care. Inspect for damage too: flattened or split cartridge pleats, channels or mud-balls in a sand bed, and torn DE grids all mean replacement, because a damaged filter lets dirt straight through.

When you replace a filter (or are sizing a new one), bigger is better: more filter area means longer runs between cleanings and finer filtration. The pool filter guide covers cartridge, sand, and DE sizing, and keeping cleanings on the pool maintenance schedule is what keeps the water clear between them.

Frequently asked questions