What is inside the filter, and how fine it actually filters

What each medium is

Sand is graded silica in a pressure vessel. Water is pushed down through the bed and particles lodge in the spaces between grains. It is cleaned by reversing the flow to lift the bed and send the trapped dirt to waste — the procedure in our backwashing guide — and the media itself lasts several seasons before it needs changing.

Glass media is recycled glass processed to a similar grade and used as a direct substitute for sand in the same vessel. Its nominal filtration is finer, it is lighter for the same volume, and it typically lasts longer. It costs more up front.

Cartridge media is pleated fabric in a housing. The pleating gives a large surface area in a small unit, and it traps finer particles than sand. It cannot be cleaned in the way a sand bed can — it is rinsed, and eventually replaced.

Fineness, and why it matters less than it sounds

Cartridge media traps smaller particles than sand, which is a genuine advantage and the reason a cartridge pool can look visibly clearer. But the practical picture is more complicated, because filtration performance changes as media loads.

A sand bed actually filters slightly finer as it loads, because the trapped material narrows the gaps — up to the point where the flow drops and it needs backwashing. A cartridge loads the other way: it starts fine and progressively restricts flow, and past a certain point rinsing no longer restores it.

Which means the honest comparison is not medium against medium, it is a well-maintained system against a neglected one. A rinsed-on-schedule cartridge outperforms an unbackwashed sand bed comfortably, and the reverse is equally true. Our cloudy water guide keeps arriving at the same conclusion for that reason.

What each one costs you across a season

This is where the choice actually bites, and the two media charge you in different currencies.

Cartridge costs parts. Intex guidance for Type A cartridges is replacement roughly every two weeks in heavy use, which is eight or nine across a 17-week season. Buying them singly is where this line gets expensive; multipacks bring the per-unit cost down substantially. Our cartridge guide covers stretching the interval honestly, and the replacement parts guide puts it in the annual budget.

Sand costs water. Every backwash sends water to waste and you refill from the tap, which also dilutes chlorine, stabilizer and alkalinity. At the EPA WaterSense national average of $6.06 per 1,000 gallons the water is not expensive, but the re-balancing is a recurring nuisance and the media still needs replacing every few seasons.

Changing sand or glass media

Sand does eventually need replacing rather than backwashing, because the grains round off with use and channels form through the bed — water finds the path of least resistance and stops passing through the media properly. The symptom is a filter that backwashes cleanly and still leaves the water hazy.

Changing it is a straightforward if messy job: drain the vessel, remove the old media without damaging the laterals or standpipe at the bottom, fill with water to cushion the drop, add the new media to the marked level, then backwash and rinse before returning to filter. Glass media drops into the same vessel and the same procedure applies, usually at a slightly lower fill weight for the same volume — follow the manufacturer’s figure rather than matching the sand weight.

What we would use, by pool size

Up to a few thousand gallons: cartridge. The hardware is cheap, the pool is small, and a sand filter is a lot of vessel for 1,700 gallons. The consumable is real but modest, and the fineness advantage is genuine.

Above about 6,000 gallons: sand or glass. This is where cartridge economics turn, because bather load and volume both push the replacement interval down while the pump runs out of published rating — Intex rates the C1000 for pools up to about 6,000 gallons. It is exactly why manufacturers bundle a sand filter with their largest pools. Our large pool equipment guide covers the threshold.

Glass over sand if you already have a sand vessel, are due a media change, and intend to keep the pool for several more seasons. It is a straight substitution with a finer nominal rating and a longer life, and it does not change the procedure.

Our sand versus cartridge comparison works the system-level decision through, and the filter roundup covers the hardware.