Which filters finer, sand or cartridge?

A cartridge: typically down to about 10 to 20 microns, against 20 to 40 for a sand bed. Glass media in a sand filter narrows the gap. Both give clear water; the difference is the last bit of sparkle, and water chemistry matters more than either filter.

How often should I backwash a sand filter?

When the pressure gauge reads about 0.3–0.7 bar (5–10 psi) above its clean reading, following the manufacturer's figure, not on a fixed schedule. In a busy summer that is typically every week or two. Backwashing more often wastes water and filters worse, because a slightly dirty bed catches finer particles.

How long does a pool filter cartridge last?

Typically one to three seasons. Rinsing before the pressure climbs too far, a soak in cartridge cleaner once or twice a season and a second set to rotate all stretch it. Replace it when the fabric frays or it no longer cleans back to its starting pressure.

Can I swap the sand in my filter for glass media?

In most sand filters, yes. Glass fills the same tank, filters finer by its makers' figures and usually lasts longer. It is lighter than sand for the same volume, so fill by the quantity the filter's maker gives for glass, not by the old sand's weight.

What about a DE filter?

Diatomaceous earth filters are the third kind: common in parts of the US, rare on private pools in Europe. They filter finest, down to a few microns, but every backwash means adding fresh DE powder, a fine dust you should not breathe, and some places restrict where the spent powder may go. For most homeowners, sand or a cartridge is the easier life.

Sand filter vs cartridge filter

The two usual pool filters compared: how fine each one filters, backwashing against the hose, the water and money each costs, and who each suits.

Zsolt Kocsmarszky · Updated September 27, 2026

A sand filter and a cartridge filter clean the water about equally well; where they really differ is the job of cleaning the filter itself. In a sand filter the pump pushes the water down through a bed of graded sand in a tank, and the dirt stays in the sand. In a cartridge filter it passes through pleated polyester fabric wrapped round a core, and the dirt stays on the fabric. One is cleaned by running water backwards through it for a few minutes, the other is lifted out and hosed down.

Which one suits you depends less on the micron figure in the brochure than on four plain questions: what your pool collects, what your water costs, where dirty water is allowed to go, and whether you would rather turn a handle or hold a hose. In the US you will find both on the same street. In most of Europe a sand filter with a multiport valve is simply what an in-ground pool gets, and cartridges turn up on above-ground and small pools. Both habits make sense for the places they grew up in.

the finest particles a clean sand bed typically holds back: 20–40 µmthe finest particles a clean sand bed typically holds back
the same for a pleated cartridge: 10–20 µmthe same for a pleated cartridge
typical life of filter sand; glass media often lasts longer: 5–7 yrstypical life of filter sand; glass media often lasts longer
typical life of a cartridge, depending on its size and load: 1–3 seasonstypical life of a cartridge, depending on its size and load

At a glance

	Sand filter	Cartridge filter
Catches particles down to	~20–40 microns; glass media finer	~10–20 microns
Cleaning it	Backwash: turn the valve, 3 minutes	Lift out and hose down, 20 minutes
How often	Every week or two in season	Every few weeks, plus a soak
Water per clean	Several bathtubs' worth, to the drain	What the garden hose uses
What wears out	Sand every 5–7 years, glass longer	Cartridges every 1–3 seasons
Leaves, pollen, a green spring	Shrugs them off	Clogs fast; keep a spare set
Upfront	Usually the cheaper tank	Usually dearer, and cartridges recur
Best for	Most family pools, trees, low effort	Small pools, dear water, no drain nearby

How each one catches dirt

A sand filter works in depth. Water enters at the top of the tank, spreads over a bed of specially graded filter sand (in the US it is sold as #20 silica), and leaves through slotted laterals at the bottom. Dirt lodges between the grains all the way down, not only on top. A clean bed holds back particles down to roughly 20 to 40 microns, and it improves as it loads up, because the trapped dirt narrows the gaps; that is why backwashing out of habit makes the water worse rather than better. Glass media, crushed recycled glass that fills the same tank in place of sand, is rated finer by its makers, often 10 microns or better.

A cartridge works on its surface. Water passes through the pleated fabric from outside to in, and the fabric holds back particles down to roughly 10 to 20 microns. The pleats fold a surprising amount of fabric into a small canister, and that area is what you are really buying: a cartridge that is generous for the pool goes weeks between cleanings, and one that is undersized clogs after a busy weekend.

What the numbers mean in the water: somewhere around 40 microns the eye stops making out single particles, so both filters give you clear water. The cartridge's finer figure shows as a little more sparkle, not as the difference between cloudy and clear. Cloudy water is almost always chemistry or too little turnover, and no filter fixes either on its own.

Cleaning the filter, and what a Saturday looks like

A sand filter is cleaned by backwashing, and the pressure gauge tells you when: once it reads about 0.3–0.7 bar (5–10 psi) above where it sat with a clean filter, whatever figure the manufacturer gives. Switch the pump off, turn the multiport valve to Backwash, run the pump for two or three minutes until the sight glass runs clear, switch off, turn to Rinse for half a minute so the bed settles, and go back to Filter. It takes five minutes and you never touch the dirt. In a busy summer that is every week or two; after a storm, a party or a spring opening it comes sooner.

A cartridge filter is cleaned by hand. Switch off, open the air bleed, undo the clamp or the lid, lift the cartridge out and hose it down from the top, pleat by pleat, with a fan nozzle rather than a pressure washer, which frays the fabric. Put it back, close up, bleed the air and restart. Allow twenty minutes and wet shoes. Every few weeks in season is typical, and once or twice a season the cartridge wants an overnight soak in cartridge cleaner to lift the sunscreen and body oils a hose leaves behind.

The habit every cartridge owner arrives at sooner or later is a second set. Swap the dirty cartridge for the clean one, and rinse and soak the dirty one when it suits you rather than with the pump off and the pool waiting. It also answers the one practical catch: hosing is an outdoor job, and equipment in a basement means carrying a dripping cartridge up the stairs.

When you winterize, the two part ways once more. A sand filter is backwashed, drained through the plug at the bottom of the tank and left with its valve in the Winter position if it has one; the sand stays where it is. A cartridge comes out, gets its deep clean and spends the winter dry and indoors, which is also when you find out whether it will manage another season.

The water that goes down the drain

Backwashing is the sand filter's one real cost. Every backwash sends the pump's full flow to waste for two or three minutes, typically 79–264 gal (300–1,000 litres) depending on the size of the filter and the pump. Every week or two through a summer, that adds up to 793–3,963 gal (3–15 m³) a season: water you pay for, then heat and treat all over again. Backwashing only when the gauge says so keeps it down; nothing makes it zero. A cartridge rinse runs a garden hose for ten or fifteen minutes, every few weeks rather than every week, and the pool itself loses nothing: no warm, treated water leaves it.

Where backwash water may go is a local rule, and worth checking before you choose. It carries chlorine and whatever the filter caught, so many places want it in the sanitary sewer rather than a storm drain, the street or a neighbour's lawn. Where water is scarce, the backwash itself is the strongest argument for a cartridge, which needs none. If the equipment sits below the sewer line, the backwash needs a pump to lift it. A cartridge filter needs no drain connection at all, only a tap and somewhere outside to hose it.

The backwash isn't pure waste, though. For many pools it is the only regular water change they get. A pool that never backwashes never dilutes, and if you use stabilized chlorine tablets, the stabilizer, cyanuric acid, climbs all season until the chlorine stops working well; sooner or later part of the water has to be replaced anyway. Cartridge owners on tablets should test for it. With a salt system or unstabilized chlorine it matters much less.

A leaf net leaning on a pool's coping beside a robot cleaner's cable and a lifted skimmer lid.

What wears out, and what it costs

A sand filter wears two things: the sand and the valve. Filter sand lasts five to seven years before its grains round off and it starts to clump or channel, and changing it is an afternoon with a wet-dry vacuum. For most residential tanks that is roughly $50 to $250 of sand, or two to four times that for glass media. The multiport valve's spider gasket wears too: a valve that keeps trickling to waste while set to Filter usually needs a new one, and the gasket is cheap where a whole valve is not.

A cartridge filter wears the cartridge. It lasts one to three seasons, depending on how big it is for the pool, how much it has to catch and how it is treated, and it is finished when the fabric frays, an end cap cracks, or it no longer cleans back to its starting pressure. A replacement costs roughly $60 to $200 for a single large element, or $250 to $700 for the four-element set a big filter takes, depending on the brand. Over ten years that is usually more than the sand, and the second set belongs in the sum.

On money alone the two are closer than either camp admits. A sand filter is usually the cheaper tank to buy and a little cheaper to own. A cartridge claws some of it back where water and sewer charges are high, and with a variable-speed pump: a clean cartridge and no multiport valve give the pump less to push against, which shows on the bill at low speed and barely at all on a single-speed pump.

Leaves, pollen and a green spring

Heavy loads are where sand earns its reputation. The bed has a lot of room between its grains and is clean again in three minutes, so a pool under oaks in October, a week of pollen in May or a green pool at opening is a nuisance rather than a crisis: filter, backwash, filter again. A cartridge meets the same load with a surface that blinds over. Clearing an algae bloom through one can mean pulling it out and hosing it every day until the water clears, and dead algae and oils are exactly what shorten a cartridge's life.

The multiport valve has one more use owners come to value. Its Waste setting sends what the vacuum picks up straight to the drain without passing through the sand, which is how a heavy mess, or a flocculant that has settled overnight, comes off the floor. A cartridge filter has no such setting unless the plumber adds a valve for it, and flocculant must never go through a cartridge: it glues the pleats shut.

Light loads are where the cartridge shines. A pool under open sky, covered most nights and cleaned by a robot, gives it little to catch, and a well-sized cartridge then runs for weeks and polishes the water a shade brighter than sand. If your pool sits under trees and opens green every spring, the sand filter's backwash is the kinder routine.

Choose sand if… choose a cartridge if…

Choose sand if you want the least hands-on routine, the pool sits under trees or tends to open green, you like being able to vacuum to waste and use a flocculant, and the backwash water has somewhere it is allowed to go. It is the default for good reasons. Ask for glass media instead of sand if you want finer water from the same tank.

Choose a cartridge if water is dear or backwashing is restricted where you live, there is no drain near the equipment, or the pool is small, covered and robot-cleaned so the load stays light. Size it generously, buy a second set of cartridges on day one, and put a tap within reach of the filter. Either way the filter is sized from the pool's volume and turnover, so draw the pool to scale in the free designer first: the volume it reports is the number the pump and the filter are chosen from.

Our take

Sand is the calm default: turn a handle every week or two, change cheap media every five to seven years, and let it shrug off leaves and a green spring. Take a cartridge when water is dear or backwashing is restricted, when there is no drain near the equipment, or when the pool is small and lightly used, and buy a second set of cartridges on day one.

Frequently asked questions

Which filters finer, sand or cartridge?: A cartridge: typically down to about 10 to 20 microns, against 20 to 40 for a sand bed. Glass media in a sand filter narrows the gap. Both give clear water; the difference is the last bit of sparkle, and water chemistry matters more than either filter.
How often should I backwash a sand filter?: When the pressure gauge reads about 0.3–0.7 bar (5–10 psi) above its clean reading, following the manufacturer's figure, not on a fixed schedule. In a busy summer that is typically every week or two. Backwashing more often wastes water and filters worse, because a slightly dirty bed catches finer particles.
How long does a pool filter cartridge last?: Typically one to three seasons. Rinsing before the pressure climbs too far, a soak in cartridge cleaner once or twice a season and a second set to rotate all stretch it. Replace it when the fabric frays or it no longer cleans back to its starting pressure.
Can I swap the sand in my filter for glass media?: In most sand filters, yes. Glass fills the same tank, filters finer by its makers' figures and usually lasts longer. It is lighter than sand for the same volume, so fill by the quantity the filter's maker gives for glass, not by the old sand's weight.
What about a DE filter?: Diatomaceous earth filters are the third kind: common in parts of the US, rare on private pools in Europe. They filter finest, down to a few microns, but every backwash means adding fresh DE powder, a fine dust you should not breathe, and some places restrict where the spent powder may go. For most homeowners, sand or a cartridge is the easier life.

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