Cloudy water despite the correct chlorine level is often a sign that the filter needs attention. When you know how to clean a pool filter properly, you not only get clearer pool water - you also reduce the load on the pump, keep energy consumption down, and extend the life of the entire treatment system.
The pool filter captures what swimmers, wind, and garden life bring with them: pollen, leaves, skin residue, sunscreen, and very small particles. In a Swedish garden, the load can change quickly, especially during pollen season or after heavy rain. That is why it is not enough to simply check the water values. The filter needs proper maintenance for the pool to remain a comfortable and hygienic meeting place for the family.
Start by identifying your pool filter
The cleaning method depends on which type of filter your pool has. The most common options are sand filters, filters with filter glass, and cartridge filters. Sand filters and filter glass are normally housed in a filter tank and are cleaned primarily by backwashing. Cartridge filters contain one or more removable filter cartridges that are rinsed clean manually.
Check the manual for your system if you are unsure. It is especially important to know the positions of the valve and the pump's recommended flow rate. An incorrect valve position or operating it while the pump is running can place unnecessary strain on both the valve and the system.
Before you begin, always switch off the circulation pump. Then carefully open the vent or the pump basket lid to release any pressure in the system. Work calmly and check that the valves are set correctly before starting the pump again.
How to clean pool filters with sand or filter glass
Sand filters and filter glass are appreciated because they handle heavy loads and provide easy ongoing operation. Filter glass can often capture smaller particles than traditional filter sand, but both materials need regular backwashing. Backwashing reverses the water flow through the filter tank so that the dirt is carried out to the drain or a designated flushing point.
When is it time to backwash?
The clearest benchmark is the pressure gauge on the filter tank. Note the pressure when the filter has just been backwashed and is clean. When the pressure has then risen by about 0.2 to 0.3 bar, it is usually time to backwash. How often this happens depends on the size of the pool, how much it is used, and how much dirt ends up in the water.
You may also notice that the inlets have poorer flow, that the vacuum loses suction or that the water becomes harder to get completely clear. Do not wait until circulation has almost stopped. A dirty filter creates higher resistance, which makes the pump work harder.
Backwash in the correct order
Switch off the pump and turn the multiport valve to the Backwash position. Then start the pump and let it run until the water in the sight glass becomes clear. This often takes about two to three minutes, but the time varies between systems and how dirty the filter is.
Then switch off the pump again and turn the valve to Rinse or Post-rinse. Run the pump for about 20 to 30 seconds. This step is short but valuable, because it repacks the filter bed and reduces the risk that dirty water will return to the pool when normal filtration starts.
Switch off the pump once more, turn the valve to Filter, and then start the system. Check that the pressure has returned close to your normal starting value and that the water level in the pool is still sufficient. Backwashing uses some water, so top up as needed.
Do not backwash unnecessarily. Too frequent backwashing wastes both water and heated energy. In addition, a filter bed often works best once it has collected a small amount of particles. Let pressure and water quality guide you rather than an overly rigid weekly schedule.
Cleaning cartridge filters without damaging the filter fabric
A cartridge filter is common in smaller pools, above-ground pools, and certain mini pools. It can provide very fine filtration, but the cartridge needs cleaning when the flow decreases or when pressure rises. During the high season, a quick weekly check can be sensible, especially if the pool is used often.
Switch off the pump, close the valves if your system has them, and open the filter housing according to the manufacturer's instructions. Lift out the cartridge and inspect the pleats. Remove larger leaves and dirt by hand before rinsing it.
Use a garden hose with a gentle to medium spray and rinse between the pleats from top to bottom. Keep the nozzle at a suitable distance. A pressure washer or a water jet that is too strong can damage the filter fabric and shorten the cartridge's service life.
If the cartridge has grease, limescale, or a coating that does not come off with water, it may need to be soaked in a cleaning agent intended for pool filters. Follow the dosage carefully and rinse the cartridge very thoroughly afterward. Common household chemicals are rarely a good choice, as they can damage the material or affect the balance of the pool water.
If possible, let a cleaned spare cartridge dry while the other is in use. With two cartridges, you can swap quickly and give each filter a proper cleaning without having to interrupt the swimming season longer than necessary.
Deeper cleaning when backwashing is not enough
Backwashing removes loose dirt, but not always limescale, oils, and very fine deposits in the filter material. If pressure rises quickly again after a backwash, or if the water remains hazy despite well-balanced water values, the filter may need a deeper cleaning.
For sand filters and filter glass, a cleaning agent designed for filter tanks is used. The agent is allowed to work according to the product instructions and is then rinsed out through a longer backwash and post-rinse. Always check that the agent is suitable for your specific filter material. Filter glass and sand have different properties, and the right product makes a difference to the result.
The sand in a sand filter does not need to be replaced every year. Often it can work for several seasons, but the intervals depend on water quality, use, and maintenance. When the grains have become rounded, clumped together, or when filtration no longer works despite proper cleaning, it is time to replace the material. Filter glass often has a long service life, but even there you should check the condition of the material when the system is serviced.
Common mistakes that impair filtration
The most common mistake is changing the valve position while the pump is running. Always switch off the pump first. Another is waiting too long before cleaning, which can lead to both poorer water quality and unnecessary wear on the pump.
Many also focus only on the filter when the water becomes cloudy. Filtration, circulation, and water chemistry must work together. A clean filter cannot compensate for an incorrect pH value, too little disinfection, or too short a circulation time. Likewise, extra chemicals will not solve the problem if the filter is clogged.
Do not forget the prefilter at the pump. The pump basket catches larger debris before the water reaches the main filter and should be emptied regularly. A clean basket improves flow and ensures that the main filter handles the right type of particles.
Adapt maintenance to the season
During early summer, pollen may require more frequent cleaning, while midsummer often means more load from swimmers and sunscreen. If you have a pool enclosure it reduces the amount of leaves and other coarse debris that reaches the water, but the filter still needs to be maintained. A pool enclosure works best together with regular circulation and a well-maintained purification system.
At spring opening, it is wise to check the filter material, seals, pressure gauge, and valve function before the load increases. Before winter shut-down, the system should be cleaned according to the conditions of the system, so that dirt is not left in the filter and pipes during the cold period.
A well-maintained filter system is rarely noticed in everyday life - and that is exactly the point. When the water stays clear, the pump runs smoothly, and the pool always feels ready for an impromptu evening swim, you have more time for garden life and less time troubleshooting. If you are unsure about the filter type, maintenance needs, or how your system should be adapted for the season, Pooltime can help you find a reliable solution that suits your pool.
