If you own a swimming pool in Cape Town, chances are it runs on a sand filter. They are the workhorse of residential pool filtration across the Western Cape — affordable, reliable and easy to live with once you understand how they work. Whether your pool sits in the wind-swept southern suburbs or catches leaves from a garden in the northern suburbs, a well-maintained sand filter keeps the water clear and swimmable all year round. This guide walks you through the essentials so you can look after yours with confidence.
How a Sand Pool Filter Works
A sand filter is a large tank filled with specially graded filter sand. Your pool pump pushes water into the top of the tank, and as it travels down through the bed of sand, dirt, debris and fine particles get trapped between the grains. The clean water then returns to your pool through the laterals at the bottom of the tank. It is a simple mechanical process, but it does a remarkable job of catching everything from leaves and insects to particles as small as 20 to 40 microns.
The multiport valve on top of the filter is the brain of the system. It lets you switch between filtering, backwashing, rinsing and other settings. Understanding these positions is the single most useful skill for any pool owner, because using the wrong setting at the wrong time is one of the most common mistakes we see.
Backwashing: The Most Important Routine
Over time the sand bed clogs with trapped debris and the filter’s pressure rises. When the pressure gauge climbs roughly 30 to 50 kPa above its clean starting point, it is time to backwash. Backwashing reverses the flow of water through the tank, lifting and flushing the dirt out to waste.
Here is the basic routine:
- Switch off the pump before turning the multiport valve — never move the valve while the pump is running.
- Set the valve to “Backwash” and run the pump until the sight glass runs clear, usually one to two minutes.
- Switch off, set the valve to “Rinse”, and run for another 20 to 30 seconds to settle the sand bed.
- Switch off and return the valve to “Filter” for normal operation.
In Cape Town, be mindful of water restrictions when backwashing, since it does send water to waste. Backwashing only when the pressure genuinely calls for it strikes the right balance between clean water and responsible use.
Choosing and Replacing Filter Media
Traditional silica sand is the standard media and typically needs replacing every five to seven years, as the grains eventually wear smooth and lose their ability to trap dirt. Many Cape Town owners are now switching to glass filter media, which is made from recycled glass and can filter finer particles while using less water to backwash. Zeolite is another alternative that offers excellent clarity.
Signs Your Sand Needs Changing
Watch for cloudy water that will not clear despite balanced chemistry, very short intervals between backwashes, or sand appearing on the pool floor. Any of these can mean the media is worn or the internal laterals have cracked and need attention.
Common Problems and How to Avoid Them
Sand filters are forgiving, but a few issues crop up regularly. Sand in the pool usually points to a broken lateral or standpipe. Water leaking from the waste line during filtering often means a worn multiport valve spider gasket. Persistently high pressure that a backwash does not fix can indicate channelling or calcified sand, especially in Cape Town’s harder water areas.
Good filtration also relies on the surface you are filtering. A rough, deteriorating pool interior sheds more debris and puts extra load on the filter. If your pool shell is showing its age, upgrading to a durable finish like fibreglass pool lining or fresh marbelite resurfacing makes a real difference to how easily your water stays clear.
When to Call a Professional
Routine backwashing and sand changes are well within reach of most owners, but cracked laterals, valve replacements and full media swaps are quicker and cleaner in experienced hands. If you are renovating your pool or the filtration simply is not keeping up, it is worth having the whole system assessed rather than replacing parts piecemeal.
At Aquatic Pools we help Cape Town pool owners get the most from their equipment alongside our lining and resurfacing work. If your filter is struggling or your pool interior needs attention, get in touch with our team for honest advice tailored to your pool. A little care goes a long way toward crystal-clear water through every Cape Town summer.
