Changing filter sand: how often to do it and which media to choose

What filter sand actually does

The sand filter is the lung of the pool. Water enters at the top, passes through the filter bed and leaves through the lateral arms at the bottom, dropping suspended particles on the way. Silica sand in good condition holds back particles of roughly 20 to 40 microns: enough for crystal-clear water, provided the media is clean and the grain edges are intact.

That is exactly the point. Sand does not "run out" by disappearing; it loses its two essential qualities: the grain edges round off after years of backwashing, and the pores between grains clog with body oils, sun cream, organic matter and limescale. When that happens, the water stops being filtered properly even though the equipment appears to run normally.

How often should the sand be changed?

There is no single figure, because it depends on use, climate and how well the water is treated. As a working reference:

• Private family pool: every 4 to 5 years. The most common interval for homes on the Costa Blanca.
• Heavy use, holiday rental or community pool: every 2 to 3 years. More bathers means a far higher organic load.
• Very hard water or repeated algae incidents: bring the change forward. Limescale cements the sand and repeated shock treatment wears it out sooner.

An important caveat: the calendar is only a guide. What really decides is the actual condition of the filter, and that is read from the signs below.

Types of filter media: what to choose

Silica sand

The traditional standard and the cheapest option. Washed, graded silica is used, normally 0.4–0.8 mm as the main filtering layer plus a bottom layer of 1–2 mm or fine gravel to protect the laterals. It filters down to around 20–40 microns and lasts about 4 or 5 years. Its weak point is that it tends to cement with grease and limescale.

Glass media (activated recycled glass)

The alternative that has grown most in recent years. It is made from crushed and treated recycled glass, and brings clear advantages:

• Finer filtration, in the order of 10–15 microns, with visibly clearer water.
• A negative electrostatic charge on the grain surface, attracting very fine particles that silica lets through.
• It does not compact or cement, because glass does not hold biofilm as readily.
• Much longer service life: 6 to 10 years with normal maintenance.
• Lower water use when backwashing, since cycles are shorter.
• Around 20 % less weight than silica for the same filter, reducing the load on the vessel.

In exchange, the purchase price is higher, although cost per year of service usually favours glass.

Zeolite

A natural volcanic mineral (clinoptilolite) with an enormous microporous structure. It filters finer than silica —around 3–5 microns— and offers something no other media does: it captures ammonium and chloramines from the water by ion exchange. That makes it very interesting for pools with a heavy bather load or recurring smell problems, exactly the ones described in our article on chloramines and urine in pools. Service life is 3 to 5 years, it needs slightly more frequent backwashing and, periodically, regeneration with brine.

AFM and activated media

AFM (Activated Filter Media) is glass media put through an extra activation process that multiplies its specific surface area. It filters below 5 microns, resists biofilm very well and is the longest-lasting media on the market, with a service life that can exceed ten years. It is the premium option, particularly suited to heavily used pools.

Anthracite and multilayer filters

Anthracite is used as a top layer in multilayer configurations: it holds back coarse particles and lets the silica layer below refine the filtration. It improves performance and lengthens cycles, but is more common in large installations than in private pools.

How much media the filter takes

The correct quantity is always on the manufacturer's plate, but the general rule is to fill two thirds of the filter body, leaving the top third free as an expansion chamber. That space is essential: without it, backwashing cannot expand the bed and the cleaning simply does not work.

• Never cover the top diffuser or force in more media than specified.
• A gravel layer at the bottom only if the manufacturer specifies it, to spread the flow and protect the laterals.
• With glass media, reduce the weight by around 20 % compared with silica: it occupies the same volume but weighs less.

The media change, step by step

• Stop the pump and close the valves on suction and return, and isolate the electrical supply.
• Drain the filter through the bottom drain plug and let it run off.
• Open the lid and remove the sand, normally with a vacuum or by hand; it is heavy work, as a domestic filter can hold between 75 and 200 kg.
• Protect the central pipe with tape or a plug so no sand falls into the laterals.
• Inspect the inside: broken laterals, a cracked central pipe, a perished lid gasket and wear on the multiport valve.
• Clean the filter body with pressurised water before loading the new media.
• Half-fill the filter with water before pouring in the media: it cushions the fall and prevents broken laterals.
• Load and level the sand evenly, without heaping it against the central pipe.
• Refit the lid with a new gasket if it shows any deformation.
• A long first backwash, three to five minutes, followed by a rinse, to flush out factory fines before sending water back to the pool.
• Note the pressure with the filter clean: that becomes the reference for knowing when the next backwash is due.

Maintenance between changes

Good maintenance noticeably extends the life of the media:

• Backwash when pressure rises 0.3 to 0.5 bar above the clean-filter reference, not by the calendar.
• Always finish with a rinse before returning to filtration, to settle the bed.
• Degrease the filter once a year with a specific product that dissolves grease and biofilm.
• Monitor hardness and limescale, especially in Alicante, where hard water speeds up cementing.
• Keep free chlorine steady so colonies cannot establish inside the filter.

At AquaGarden Alicante we carry out full media changes, including inspection of laterals, gasket and multiport valve, and we advise whether it is worth staying with silica or moving up to glass media. See our pool repair and pool maintenance services, from El Campello to Elche.