Filter cartridges: the consumable nobody budgets for

What the cartridge is doing

A cartridge filter is a pleated media element in a housing. Water is pushed through it, particles are trapped in the pleats, and clean water goes back to the pool. As it loads up, the resistance rises, the system flow rate falls, and the pump that was turning your water over in three and a half hours is now taking five. Nothing announces this; the water just gradually stops being clear.

Type A is the most common format in this category, which is genuinely useful — it means replacements are cheap and easy to find, and multipacks bring the per-cartridge cost down considerably. It also means it is easy to buy the wrong thing, because “Type A” describes a size and shape rather than a quality level.

The interval, and how to know yours

Intex guidance for Type A cartridges is replacement roughly every two weeks in heavy use. That is a starting point rather than a law, and your own interval depends on how much the pool is used, how much organic material lands in it and whether you skim daily.

The practical signal is simpler than a calendar. When a rinse no longer restores the flow — when the water coming back into the pool is visibly weaker the day after you cleaned the cartridge — the media is loaded beyond recovery and it is time for a new one. A cartridge that looks gray rather than off-white after rinsing is telling you the same thing.

The cloudy-water connection

If your water is cloudy and your chemistry tests fine, the cartridge is the first thing to check and it is right the large majority of the time. This is worth knowing because the alternative diagnosis costs money: people buy clarifier, shock and algaecide to solve what is mechanically a blocked filter.

Worse, a clarifier is actively wasted on a loaded cartridge. Its whole function is to clump fine particles so the filter can catch them, so dosing one into a system that cannot filter is money poured into the pool. Change the cartridge first, run the pump, and see whether you still have a problem — our cloudy water guide and clarifier guide both start from the same place.

The cartridge treadmill versus a sand filter

This is the real strategic question, and it is a cost question rather than a performance one. A cartridge system is cheap to buy and has a consumable attached to it for as long as you own it. A sand filter costs more up front, uses media that lasts several seasons, and is backwashed rather than replaced — so its running cost is water and electricity rather than parts.

At the small end of this category the cartridge usually still wins, because the pool is small, the season is short and a sand filter is a lot of hardware for 1,700 gallons. As volume rises the sums move, which is why Intex bundles a sand filter with the 18-foot Ultra XTR rather than a cartridge pump. Our sand versus cartridge comparison works through it properly, and the maintenance cost guide puts the consumable alongside the other recurring lines.

Getting more life out of each one

Three habits stretch the interval without compromising the water. Skim daily, because anything you remove while it floats is something the cartridge never has to catch. Rinse on a schedule rather than waiting for the flow to drop, since surface loading is easy to remove and deep loading is not. And keep two cartridges in rotation, rinsing one and drying it fully while the other is in the housing — a properly dried cartridge rinses cleaner next time.

Sizing matters too. An undersized pump running against a loading cartridge falls below useful turnover faster than a correctly sized one does, so if you are permanently on the edge, the fix may be the pump rather than the cartridge. Our pump sizing guide has that arithmetic.

For which cartridge to buy, how many a season actually takes and why multipacks are the only sensible way to order them, see our filter cartridge roundup.