Choosing a Pool Filtration System: Sand, Cartridge, DE and Activated Glass

Every pool filter traps dirt. What separates one from another is how small a particle it catches, and how much water it wastes doing so. Those two things decide whether your water looks merely clean or actually clear, and they are rarely the things owners are asked about when a system is specified.

We have been installing and replacing filtration systems on pools across this region since 2008. What follows is how the options compare on the measures that matter here.

Why does the filter matter more than most owners think?

Because the filter decides how hard everything else has to work. Organic matter the filter removes is organic matter your chlorine never has to oxidise, so a better filter means lower chemical demand, clearer water and less corrective work. A poor filter passes that load straight back into the pool, and you pay for it in chemicals.

In this climate the load is heavy: long swimming seasons, high bather numbers on rental properties, and the fine Saharan dust that arrives on the wind and passes through anything coarse. A filter that copes in a northern European garden will not necessarily cope here.

How is filter performance actually measured?

By particle size, in microns. A micron is a thousandth of a millimetre, and a filter's rating describes the smallest particle it reliably traps. The number matters because the difference between clean-looking and genuinely clear water lies in the range between 1 and 20 microns, which is exactly where filter types differ.

The second measure is turnover: how long the pump takes to pass the entire pool volume through the filter once. Most residential pools turn over in 6 to 8 hours, and in high summer 8 to 12 hours of running is normal here.

What are the main types of pool filter?

Sand

The workhorse. A bed of graded silica sand traps debris as water passes through, and backwashing flushes it out. Good-quality silica sand removes 95 per cent of particles above 20 microns, the sand bed lasts around five to seven years, and the whole thing is forgiving of neglect, which is why most pools here have one.

The cost is water. Every backwash sends hundreds of litres to waste, which in a region with recurring water restrictions is worth counting.

Cartridge

A cartridge filter uses a pleated element with a large surface area, and typically catches particles down to 10 to 15 microns. Cartridge filters use no backwash water at all, which is their strongest argument here. In exchange, they need hosing down every few weeks through the season, and the element itself needs replacing every year or two.

Diatomaceous earth

Diatomaceous earth is the finest conventional option, filtering down to 2 to 5 microns by coating a grid in fossilised diatom powder. The water clarity is genuinely superior, but the maintenance burden is heavier: the filter must be recharged with fresh powder after every backwash, and the handling is fiddly enough that we rarely specify DE for a private pool whose owner is away half the year.

Is glass media better than sand?

Substantially, and it goes into the filter you already own. Activated filter media, made by upcycling green and brown glass bottles, replaces the sand in a standard filter with no other changes to the system. Dryden Aqua's AFM removes 95 per cent of particles above 1 micron, against 95 per cent above 20 microns for good silica sand, and holds that performance for more than ten years without replacement (Dryden Aqua), with the figures independently verified by IFTS.

So glass media catches particles roughly twenty times smaller, simply by emptying one filter and refilling it. It is the single best-value upgrade in pool filtration, and the reason we fit it as part of the advanced water treatment systems we supply.

The knock-on effects matter as much as the clarity. Finer filtration means less organic load reaching the water, which means lower chlorine demand, and glass media resists the biofouling that turns an old sand bed into a place where bacteria live rather than a place where they are removed.

Which filter suits your pool?

Start from how the pool is used rather than from the filter catalogue. A family pool with an owner on site suits sand or glass media, because backwashing is a two-minute job for someone who is there. A holiday rental suits glass media or cartridge, because both reduce how often anyone has to intervene. A pool with a serious clarity requirement, or one recovering from years of poor filtration, justifies DE.

Water is the tie-breaker in this region. If you are choosing between two systems and one of them backwashes, count what that costs across a summer before deciding.

Whatever the media, the pump matters as much as the filter. A variable-speed pump moving the same volume more slowly over longer hours uses a fraction of the electricity of an old single-speed unit, and slower flow filters better, because the water spends longer in contact with the media.

When is it worth upgrading?

When the water stays cloudy after a proper backwash, when the pressure climbs faster each week, or when you find yourself adding chemicals to solve what is actually a filtration problem. Sand that has channelled lets water find a path straight through, and no amount of chlorine compensates for a filter that has stopped filtering.

Age alone is a reason to look. A sand bed more than seven years old is doing less than its owner assumes, and that is the natural point to swap it for glass media.

Get in touch

If you are unsure which filter your pool has or whether it is still doing its job, we will look at it and tell you. Sometimes the answer is a media change, sometimes a new pump, and sometimes nothing at all.

Get in touch.

Frequently asked questions

Which pool filtration system is best for a new pool owner?

A sand filter is the usual starting point because it is forgiving, cheap to run and needs little attention. Filling it with activated glass media instead of sand costs a little more at the outset and lets the same filter catch far finer particles. It is the upgrade most new owners wish they had made first.

How do I know when my pool filter needs attention?

Watch the pressure gauge rather than the calendar. A rise of around 0.5 bar above the clean reading, or whatever rise your filter manufacturer specifies, means it is time to backwash or clean the element. Water that stays cloudy after a normal backwash usually means the media has channelled and needs replacing.

Can a good filter replace pool chemicals?

No. Filtration removes particles, while disinfection kills micro-organisms and oxidises dissolved organic matter. Neither does the other's job. A better filter does reduce chemical demand, because organic matter the filter removes is organic matter the chlorine no longer has to deal with.

What do micron ratings on pool filters mean?

A micron is a thousandth of a millimetre, and the rating describes the smallest particle a filter reliably traps. Good silica sand removes 95 per cent of particles above 20 microns, while activated glass media removes 95 per cent above 1 micron, and that gap is what you see in the clarity of the water.

How many hours a day should a pool filter run?

Long enough to turn the whole pool volume over at least once, which is typically 6 to 8 hours of running, and 8 to 12 hours in high summer when demand peaks. Run those hours in daylight, when chlorine demand and bather load are highest.