How a sand filter actually works
Water from the pool is pushed down through a bed of specially graded silica sand. Dirt, dead algae and fine particles are trapped in the upper layers while clean water passes through slotted collectors, called laterals, at the bottom and back to the pool. Backwashing reverses the flow to lift the bed and flush the trapped dirt out to waste.
For that to work, the sand grains need sharp edges that trap particles, and the bed needs to be loose so water passes evenly through all of it. Age and hard water destroy both conditions. The sand becomes smooth and stops trapping fine dirt, and calcium and body oils glue it into lumps that water simply flows around.
Signs your filter sand needs changing
There is no single date on a calendar. The usual guide is every few years, sooner in a pool that is used heavily or where the water is hard, as it is across most of Gauteng. The pool itself tells you when it is time.
- Water stays dull or cloudy even when the chlorine and pH are correct
- The pressure gauge climbs back up very soon after a backwash
- Backwashing makes little difference, or needs doing far more often than it used to
- Sand appears on the pool floor near the returns — often a broken lateral
- When we open the filter, the sand is caked, cracked or has a hard crust on top
- Green pool treatments work, then the pool clouds over again within days
What the job involves
A sand change is heavier work than most people expect: the old sand has to be dug out of the tank by hand, often set hard, without damaging the laterals at the bottom. While the tank is empty we inspect the laterals and the standpipe, because a single cracked lateral lets sand into the pool and will ruin new sand quickly.
The tank is rinsed, the laterals are protected, and the new filter media goes in to the correct level. The multiport valve is refitted with its seals checked, and the filter is backwashed and rinsed to settle the bed and clear the fine dust that comes with new sand.
- Old sand dug out and removed
- Laterals and standpipe inspected
- Tank cleaned and new filter media loaded to the right level
- Multiport valve refitted, seals checked
- Backwash and rinse to settle the new bed
- Pressure checked with the pump running
Backwashing properly between sand changes
Good backwashing habits make sand last longer. Backwash when the pressure gauge reads roughly 50–70 kPa above its clean reading, not on a fixed day regardless of need. Run backwash until the sight glass runs clear, then always rinse for about half a minute so the bed settles and dirty water is not sent back into the pool.
Always switch the pump off before moving the multiport handle. Turning it under pressure damages the spider gasket inside the valve, which then leaks pool water to waste all the time. If your backwash pipe is always wet, that is probably what has happened.
Hard water, calcium and your filter
Municipal water in Centurion and Pretoria carries a fair amount of dissolved calcium. As pool water evaporates and is topped up, the calcium concentration rises, and it deposits wherever it can: on the tile line, on chlorinator cells, and inside the filter bed. Keeping pH and alkalinity in range slows it down considerably.
A filter cleaner or degreaser used once or twice a season can help between changes, but once the bed has cemented, no chemical will break it up. At that point replacing the sand is cheaper than fighting it with extra chlorine and clarifier.
Replacing the filter itself
Sometimes the tank is the problem: a cracked filter body, a split lid, or a filter that is too small for the pool so it can never keep up. We sell sand filters and cartridge filters in our online shop and install them at a fixed fitting price. Quoting a replacement filter costs nothing.
A filter and pump have to be matched. Fitting a large pump to a small filter pushes water through the sand too fast and filters worse, so if we replace one we check the other.
How it works
Identify the filter
WhatsApp 081 577 5051 a photo of the filter label. We confirm the bag count and the price.
Empty the tank
Old sand dug out by hand, taking care not to crack the laterals.
Inspect
Laterals, standpipe and valve checked while the tank is open.
Refill and settle
New media in, valve refitted, then backwash and rinse until the water runs clear.
Frequently asked questions
How often should pool filter sand be changed?
Every few years is the usual guide, sooner with heavy use or hard water. Cloudy water despite good chemistry and pressure that climbs straight back after a backwash are the signs.
How much does a pool sand change cost?
It depends on the filter size: R1,450 for a 3-bag filter, R1,550 for 4 bags, R1,650 for 5 bags and R1,750 for 6 bags.
How do I know how many bags my filter takes?
It is printed on the filter label or in the manual. If the label has faded, send us a photo of the tank and we will identify it.
Why is there sand in my pool?
Usually a cracked lateral at the bottom of the filter, which lets sand back to the pool. It can also be sand that was not rinsed after a backwash. We check laterals on every sand change.
Is the water cloudy after a sand change?
Briefly, sometimes. New sand carries fine dust, which is why we backwash and rinse before we leave. Any slight haze clears after a filter cycle or two.
How often should I backwash?
When the pressure gauge rises roughly 50–70 kPa above its clean reading, and after heavy storms. Backwashing on a fixed schedule regardless of pressure wastes water.
Do you install new filters?
Yes. We sell sand and cartridge filters in our online shop and fit them at a fixed installation price. We check the pump matches the filter before recommending one.