The filter is what actually makes the water clear. The pump only moves water; the filter removes what is in it. When a pool goes cloudy and stays cloudy despite correct chemistry, the filter is usually the reason.
Filter faults are also among the most commonly misdiagnosed, because a filter problem and a pump problem produce overlapping symptoms - and because the pressure gauge that tells you what is happening is often the first component to fail.
A filter pressure reading and a description of the water helps narrow the fault before anyone arrives.
Get a Pool Filter Repair QuoteReading the Pressure Gauge
The filter pressure gauge is the most informative and most ignored instrument on a pool. What matters is not the absolute number but the change from the clean starting pressure of that specific system.
| What the gauge shows | What it means |
|---|---|
| Pressure rising steadily over days or weeks | Normal. The filter is loading with debris. When it rises meaningfully above the clean baseline, it is due for backwashing or cleaning. |
| Pressure stays high after backwashing | Media is fouled, channelled or the wrong grade; a cartridge is clogged or degraded; or there is a restriction after the filter. |
| Pressure very low with the pump running | Restriction before the filter - blocked baskets, a partly closed suction valve, or a suction-side air leak. The filter is being starved rather than blocked. |
| Pressure climbs immediately after backwashing | Often channelling in the sand bed, or a media problem rather than a debris problem. |
| Gauge reads zero when the pump is running | The gauge itself has failed. They are inexpensive and they fail regularly, and a dead gauge means flying blind. |
| Pressure spikes sharply | Something has blocked. Stop the pump before pressure damages the filter or its connections. |
Know your clean starting pressure. The single most useful piece of information about a filter is what the gauge reads immediately after backwashing when everything is in good order. Without that baseline, no later reading can be interpreted, because a figure that is normal on one system is high on another. Note it down and put it somewhere near the plant.
Sand Filters
The most common type on domestic pools in Cape Town. Water is forced down through a bed of graded sand, debris is trapped in the bed, and clean water returns through laterals at the bottom.
Sand Blowing Back Into the Pool
Sand appearing on the pool floor, usually in a fan near a return, means the sand is getting past the laterals. The causes are cracked or broken laterals, a cracked standpipe, or a lateral that has come loose from the manifold. It is not a cosmetic problem - sand passing through the system reaches the pump impeller and wears it.
The repair means opening the filter, removing the sand, inspecting the manifold and laterals, replacing what has failed, and refilling with the correct grade and quantity of media. It is a labour-intensive job because of the sand handling rather than because the parts are expensive.
Channelling
Water finding preferential paths through the sand bed rather than passing evenly through it. The symptom is poor filtration with normal or low pressure, which is confusing because everything looks fine on the gauge. It is caused by sand that has compacted, calcified or been fouled with oils and greases.
Media Degradation
Filter sand does not last forever. Over years, the grains wear smooth and lose the sharp edges that trap fine debris, and the bed becomes progressively less effective. A pool that will not clear despite correct chemistry, adequate run time and normal pressure often has a sand bed that has simply worn out.
Calcification
In hard water, or where calcium hardness has been allowed to run high, the sand bed can cement into a solid mass. Once that happens the bed cannot be backwashed effectively and the media has to be replaced.
The Multiport Valve
The multiport is the most-handled component in the plant room and the one that most often fails. It has a rotating spider gasket that seals between positions, and that gasket wears.
| Symptom | Likely cause |
|---|---|
| Water running to waste continuously while filtering | Worn or displaced spider gasket, allowing flow past the seal. |
| Water leaking from the valve body | Failed body O-ring, cracked body, or a loose union. |
| Handle stiff or will not seat | Worn gasket, debris under the diverter, or a corroded spindle. |
| Pool will not vacuum to waste properly | Valve not seating fully in the waste position, or a spider gasket that has failed between adjacent ports. |
| Leaking from the sight glass | Perished seal on the sight glass, which is a small and inexpensive fix. |
Never move a multiport valve with the pump running. Doing so slams full system pressure against a partly open port and is the fastest way to destroy the spider gasket - and occasionally the valve body. Switch the pump off, change the position, then switch it back on. This one habit prevents most multiport failures.
A filter that will not clear the water after backwashing usually needs the media or the internals looked at.
Book a Filter InspectionCartridge Filters
Cartridge filters use a pleated element rather than a media bed. They filter finer than sand, use no water to backwash, and take up less space. Their weakness is that the element is a consumable and it has to be physically cleaned rather than backwashed.
- Pressure high shortly after cleaning usually means the element is loaded with oils and greases that rinsing does not remove. Those need chemical soaking rather than a hose.
- Debris passing through points to a torn pleat, a collapsed core, or an element that has been distorted by pressure.
- Water bypassing the element is normally a failed O-ring at the manifold or a distorted end cap - the filter appears to work while filtering nothing.
- A crushed or telescoped element means it has been run at pressure far beyond what it is rated for, which usually points to it not having been cleaned for a long time.
- Reduced life comes from cleaning with high-pressure water, which drives debris into the fabric and damages the pleats. Low-pressure rinsing and soaking is what preserves them.
DE Filters
Diatomaceous earth filters give the finest filtration of the three types, using DE powder coated onto grids. They are less common on domestic pools locally but are found on some larger and older installations.
The typical faults are torn grids letting DE back into the pool, a damaged manifold, and grids that have become caked hard and no longer accept a proper coating. DE also needs recharging after every backwash, and a filter that is not recharged is running as a very poor grid filter.
Filter and Pump Have to Match
A filter has a rated flow, and pushing more than that through it makes filtration worse rather than better. Water passing too quickly through the media does not have time for particles to be trapped, so an oversized pump on an undersized filter produces a pool that never quite clears despite everything appearing to work.
Undersized filters also load quickly, which means frequent backwashing, which on a sand filter means water down the drain each time. Where a pump is being replaced, the filter's rated flow is one of the numbers the new pump should be chosen against - see pool pump repairs.
When the Filter Is Not the Problem
Cloudy water gets blamed on the filter more often than the filter deserves. Before condemning it, rule out:
- Run time. A filter can only clean the water that passes through it. Too few hours a day and the pool never achieves a full turnover.
- Water chemistry. High pH causes calcium to come out of solution as a fine haze that a filter struggles to catch. Correct chemistry first, then judge the filter.
- Inadequate sanitiser. Cloudiness is sometimes an algae bloom in its earliest stage rather than a filtration failure.
- Circulation. Dead spots where water does not move mean debris settles rather than reaching the skimmer at all.
- A suction-side air leak. Air in the system reduces flow through the filter substantially without anything appearing wrong with the filter itself.
- Very fine particulate. Some material is finer than a sand filter can catch, and it needs a clarifier or flocculant to be filterable at all.
Repair or Replace?
| Situation | Usual route |
|---|---|
| Failed pressure gauge | Replace the gauge. Inexpensive, and it restores your ability to diagnose anything else. |
| Worn multiport spider gasket | Replace the gasket if available for the valve, otherwise the valve head. |
| Broken laterals, tank sound | Replace the laterals and media. The tank is the expensive part and it is fine. |
| Worn-out or calcified sand | Replace the media. The filter itself is not faulty. |
| Cracked or crazed filter tank | Replace the filter. A tank under pressure is not something to patch. |
| Torn cartridge element | Replace the element. They are consumables. |
| Filter genuinely undersized for the pool | Replace on performance grounds. No repair fixes being too small. |
What Affects the Cost of Filter Repairs
The cost of pool filter repairs in Cape Town depends on:
- Which type of filter it is and which component has failed
- Whether the tank has to be opened and the media removed, which is the labour-heavy part of any sand filter repair
- The volume and grade of media needed on a refill
- Parts availability for the make and model, particularly on older filters
- Access to the plant area - a filter in a confined pit takes considerably longer to work on
- Whether the filter is being repaired or replaced, and whether pipework has to be altered to fit a replacement
- Whether related work on the pump or valves is being done at the same visit
Related Pool Services
Filter work sits alongside pump and plumbing work as one of the most common requests coming through Swimming Pool Repairs Cape Town.
What Swimming Pool Filter Repairs Cost
Filter work splits into servicing, part replacement and full replacement. A sand change is routine maintenance; a cracked filter body is not repairable and needs replacing.
| Item | Indicative range | What moves it |
|---|---|---|
| Filter inspection and service | R600 – R1,500 | Access and filter type. |
| Sand change | R1,100 – R2,500+ | Filter size and how much sand it takes. |
| Multiport valve repair or replacement | R900 – R3,500 | Whether the spider gasket or the whole valve. |
| Lateral or standpipe replacement | R1,200 – R4,000 | Usually the cause of sand returning to the pool. |
| General filter repairs | R1,500 – R5,000+ | Nature of the fault. |
| Cartridge element replacement | R500 – R2,500 | Element size and quality. |
| Full filter replacement | R3,800 – R12,000 | Filter type and size; sand, cartridge or DE. |
These are indicative market ranges, not a quotation. They are compiled from published South African pool industry pricing to give you a starting point for budgeting. They are not the rate card of any company on this platform, and no figure here is a commitment by anyone.
Sand appearing on the pool floor is almost always broken laterals or a cracked standpipe inside the filter, not a fault with the sand. Adding more sand does not fix it.
Published pool pricing in South Africa varies widely — different 2026 guides quote ranges for the same job that differ by a factor of three — because pool size, surface area, access, the condition of what is already there, and how much preparation is needed all move the number. Figures generally exclude VAT unless noted, and change over time. Only an itemised written quote against your actual pool means anything.
Swimming Pool Filter Repairs FAQs
Why is sand blowing back into my pool?
Because sand is getting past the laterals at the bottom of the filter. The usual causes are a cracked or broken lateral, a lateral that has come loose from the manifold, or a cracked standpipe.
It needs attention rather than tolerating, because sand passing through the system reaches the pump impeller and wears it. The repair involves emptying the filter, replacing the failed part and refilling with the correct grade and quantity of media.
How often should pool filter sand be replaced?
There is no fixed interval, because it depends on how hard the filter has worked, the water chemistry it has handled, and whether oils and greases have fouled the bed. Sand wears smooth over years and loses the sharp edges that trap fine debris.
The practical signal is a pool that will not clear despite correct chemistry, adequate run time and normal filter pressure. That combination usually means the media has stopped filtering effectively rather than that anything is broken.
Why is my filter pressure high after backwashing?
If pressure barely drops after a backwash, the problem is not debris in the bed. Common causes are sand that has calcified or channelled, a media bed that has fouled with oils, a cartridge element that needs chemical soaking rather than rinsing, or a restriction downstream of the filter.
It is worth checking the gauge itself too. Pressure gauges fail regularly, and a faulty gauge sends people chasing a filter problem that does not exist.
Can a multiport valve be repaired?
Usually yes. The most common failure is the spider gasket, which is a replaceable part where it is still available for the valve model. Body O-rings, sight glasses and handles are also replaceable.
A cracked valve body is different - that is a pressure component and it should be replaced rather than patched. Parts availability on older valves is often the deciding factor.
Why is water running out of the waste line while filtering?
Almost always a worn or displaced spider gasket in the multiport valve, letting water bypass the seal between the filter and waste ports. It wastes water continuously and drops the pool level in a way that is easily mistaken for a leak.
The most common cause of a prematurely worn spider gasket is turning the valve while the pump is running, which slams system pressure against a partly open port.
What is the difference between backwashing and cleaning a filter?
Backwashing applies to sand and DE filters: flow is reversed through the media to lift trapped debris and send it to waste. It uses a meaningful amount of water each time, and on a DE filter the media has to be recharged afterwards.
Cartridge filters are not backwashed. The element is removed and physically rinsed, and periodically soaked in a cleaning solution to remove the oils and greases that rinsing leaves behind.
Can a filter be too big for a pool?
Oversizing a filter is rarely a problem and is often an advantage - it loads more slowly, needs less frequent backwashing, and gives lower flow velocity through the media, which improves filtration.
The mismatch that causes trouble is the opposite: too much pump for the filter's rated flow. Water passing through the media too quickly is filtered less effectively, so the pool never quite clears while everything appears to be working.
My water is cloudy but the filter seems fine - what now?
Work through the things that are not the filter first. Check run time, because a pool needs enough hours to turn its volume over. Check pH, since high pH puts calcium out of solution as a fine haze. Check sanitiser level, because early algae reads as cloudiness.
Also check for air in the pump basket, which indicates a suction-side leak reducing flow through the filter. If all of that is sound, the media has probably reached the end of its useful life even though nothing is visibly broken.
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