The sand in your pool filter does not last forever. After 3–5 seasons the grains wear smooth, clump together, and the filter stops truly cleaning the water — even with the pump running at full power and the chemistry in perfect order. Replacing the media is a single afternoon’s work you can easily do yourself: you just need to know when it is time, how much and what kind of media to buy, and what to watch out for when filling.
How do I know the filter sand is worn out?
The age of the media is only a rough guide. Silica sand typically lasts 3–5 years, filter glass considerably longer — but what really matters is the actual condition of the media and how the filter behaves. Watch for these signals:
- Lumps and channels in the sand. Open the tank lid and reach inside: if the sand is caked into hard lumps or the water has carved vertical channels through it, it flows straight through without being filtered. Lumps form from scale deposits and flocculant residues.
- Cloudy water despite correct chemistry. Your pH and sanitizer levels are within range, yet the water still is not sparkling clear. Before reaching for another dose of clarifier, check the filter media. If the cloudiness comes with a green tinge, also read our guide to fixing green pool water — algae and an exhausted filter often go hand in hand.
- Falling efficiency and weaker flow from the return jets. Clogged media creates resistance, the pressure on the gauge rises faster than it used to, and the flow weakens.
- Short intervals between backwashes. If you have to backwash every few days instead of every 1–2 weeks and the pressure only drops briefly afterwards, the sand has run out of capacity.
The smoothed grains of old sand lose the sharp edges that mechanically trap dirt. The filter then lets fine particles back into the pool — and no amount of chemicals can make up for it.
A practical test: run the filter overnight and in the morning shine a light into the water across the surface. If you can see fine particles floating in the beam even though you dosed clarifier the day before, the filter is no longer doing its job. The second clue is the pressure gauge — note the pressure after a backwash and track how many days it takes to rise by 0.2–0.3 bar. If that interval keeps getting shorter season after season, the media has reached the end of its life.
What to fill the filter with: sand, filter glass, or zeolite?
The classic choice is silica sand, grade 0.4–0.8 mm. It is inexpensive (typically around 0.6–1 €/kg), widely available and perfectly adequate for most pools. The grade is what matters: finer sand clogs quickly and escapes into the pool, while coarser sand lets dirt through. Builder’s sand or sandpit sand has no place in a filter.
Filter glass is a modern alternative made from recycled glass. It filters finer particles (around 15–20 microns versus 30–40 microns for sand), its smooth surface reduces clumping and biofilm formation, and backwashing is shorter — saving both water and energy. It lasts 10 years or more, i.e. two to three times longer than sand. It is lighter, so you need roughly 15–20% less of it than sand: where the label calls for 100 kg of sand, about 80–85 kg of glass is enough. The higher purchase price usually pays for itself thanks to the longer lifespan.
Zeolite is a natural mineral that, besides mechanical filtration, also binds ammonia compounds, helping to reduce odour and chloramines. You need less of it than sand, and it is best suited where you want maximum water quality. For a more detailed comparison of filtration technologies, including when a cartridge makes sense, see our article on sand vs. cartridge filtration.
| Media | Filtration fineness | Lifespan | Quantity vs. sand | Best for |
|---|---|---|---|---|
| Silica sand 0.4–0.8 mm | approx. 30–40 µm | 3–5 years | 100% (per label) | Standard choice, lowest price |
| Filter glass | approx. 15–20 µm | 10+ years | approx. 80–85% | Finer filtration, water savings on backwash |
| Zeolite | approx. 5–20 µm | 5–8 years | approx. 55–65% | Highest water quality, chloramine reduction |
How much media will I need?
The figure on the filter tank label or in the manufacturer’s manual always takes precedence — quantities vary by design. If the label is missing, use this rough guide based on tank diameter:
| Filter diameter | Silica sand (approx.) | Filter glass (−15–20%) |
|---|---|---|
| 300 mm | 20–25 kg | 17–20 kg |
| 350 mm | 30–35 kg | 25–30 kg |
| 400 mm | 45–50 kg | 38–42 kg |
| 450 mm | 70–75 kg | 58–63 kg |
| 500 mm | 85–100 kg | 72–85 kg |
| 600 mm | 140–150 kg | 115–125 kg |
| 750 mm | 250–300 kg | 210–250 kg |
The tank is never filled to the brim — the media should reach roughly two thirds of the tank height, leaving space above it for the media to fluidise during backwashing. On some filters the manufacturer also specifies a bottom layer of coarser sand (1–2 mm grade) around the laterals.
Changing the sand step by step
- Switch off the pump and disconnect it from the power supply. Ideally at the breaker, so no one can start it by accident.
- Close the valves on both the suction and return lines (on in-ground pools), or plug the skimmer and return jets so water cannot gravity-feed into the equipment.
- Drain the filter tank via the drain plug at the bottom. Expect several dozen litres of water to run out.
- Remove the multiport valve or the tank lid. On top-mount filters the valve is screwed or clamped directly onto the tank; disconnect the pipework and carefully lift it out together with the centre standpipe if it can be removed. We covered the functions of the individual valve positions in our article on the multiport valve of a sand filter.
- Remove the old sand. The most convenient way is a wet (workshop) vacuum, or by hand with a plastic scoop. Metal tools do not belong in the tank — they can damage the internal parts.
- Inspect the laterals at the bottom of the tank. This is the key step: the star-shaped assembly of collector laterals (arms) at the bottom tends to become brittle over the years. A cracked lateral means a permanent leak of sand into the pool, so inspect every arm, check the slots and replace any damaged parts — they are available as spares.
- Rinse out the tank with a jet of water so no sludge or remnants of the old media are left inside.
- Cover the opening of the standpipe (with a plastic bag and rubber band, or the cap from the packaging) so no media falls inside — from there it would travel straight into the pool.
- Fill the tank about one third with water and pour in the media in layers. The water cushions the impact of the grains on the laterals and helps the media settle evenly. Pour slowly and keep the centre pipe centred.
- Fit new seals. The O-ring of the valve or lid is the cheapest insurance against dripping equipment; never reuse an old, deformed seal. Mount the valve, reconnect the pipework and open the valves.
- Run a thorough backwash for 2–3 minutes, followed by a short rinse cycle. New media contains dust and abrasion debris that must go to waste — only then switch to filtration. Skip this step and the fine dust ends up in your pool.
Which mistakes should I avoid?
- Damaging the laterals while pouring. Pouring straight into an empty, dry tank is the most common cause of a cracked lateral assembly. Always water first, then sand.
- Wrong grade or unsuitable sand. Any grain size other than specified (typically 0.4–0.8 mm) means either sand in the pool or dirty water.
- Overfilled tank. Without free space the media cannot fluidise and clean itself during backwashing — the filter then clogs permanently.
- Forgetting the first backwash. Switch straight to filtration and you will drive the dust from the new media into the pool, causing cloudiness that was easy to prevent.
- Old seals and loose connections. A dripping valve after the change is almost always down to the O-ring, not your workmanship.
What to do with the old sand and when to call a professional?
Used filter sand is not hazardous waste — once it has dried out and any residual chlorine has aired off, you can use it in the garden as bedding under paving, in joints or to firm up paths. It does not belong in a children’s sandpit, however (it contains trapped dirt and microorganisms), and larger quantities are best taken to a recycling centre. Filter glass goes to a recycling centre, or to glass recycling by arrangement.
Consider calling a professional if you have a large in-ground filter (600 mm and above means handling 150+ kg of media in an often cramped pit), if the valve or tank shows cracks, or if you would rather not tackle replacing damaged laterals yourself. A professional will also check the whole system for leaks and correct settings. For common filters, the cost of a professional media change is typically around 80–200 € plus materials.
Is it worth combining the change with other maintenance?
Allow for a short “running-in” period after the change: for the first two to three days run the filter longer than usual, and do one more backwash after the first week. The new media will settle, the flow will stabilise, and the pressure gauge will give you a fresh baseline to compare against in future seasons.
Yes — the ideal time is spring before filling or autumn during winterizing, when the equipment is shut down anyway. In one shutdown you can also inspect the pump, replace the pressure gauge or lubricate the valve. To make sure regular tasks never slip your mind, use our year-round pool maintenance calendar.
Frequently asked questions about changing filter sand
How often should filter sand be changed?
Roughly every 3–5 years of operation. What really decides, though, is the condition of the media: lumps, channels, persistent cloudiness and ever-shorter intervals between backwashes are a clearer signal than age alone. Filter glass lasts 10 years or more.
Can I use ordinary builder’s sand?
No. Builder’s sand has an unsuitable and inconsistent grain size and contains clay and dust — it will either clog the filter or end up in the pool. Use only graded silica filter sand of 0.4–0.8 mm grade, or alternatively filter glass or zeolite.
Why is there sand in my pool after the change?
Most often it is a cracked lateral at the bottom of the tank (typically damaged during pouring), or too fine a grade, or a skipped first backwash. Fine dust after the change is normal and disappears after backwashing; coarse grains on the pool floor point to a mechanical fault.
Can I just clean the sand instead of replacing it?
Partly. A dedicated filter media cleaner dissolves scale and grease and extends the sand’s life — it is worth using once a season. But no chemical can restore smoothed grains, so after years of use cleaning only postpones the change, it does not replace it.
How much does media for a typical filter cost?
For a residential filter of 400–500 mm diameter, expect 50–100 kg of sand, i.e. roughly 30–100 €. Filter glass costs two to three times as much, but thanks to its two to three times longer lifespan and the water saved on backwashing, the difference usually pays for itself.
You will find new filter media, replacement laterals, seals and complete filter systems in our pool equipment category. And if you are not sure whether your filter deserves new media or it is time to replace the whole tank, we will be happy to help you choose.
