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Sand filter systems are very popular due to their compact design and lower purchase costs. If you are looking for an above-ground or permanently integrated filter system for the pool, a sand filter is a good choice.

In addition to sand filter systems, there are other types of filtration systems to clean pool water. Like any other filtration system, you need to regularly maintain a sand filtration system. The most important thing in maintaining a sand filtration system is backwashing. For this reason, we explain in this guide how to backwash a sand filtration system.

Why do you need to clean a sand filter system?

In a sand filter, the pool water is passed through a filter sand. As it passes through, the dirt gets caught in the sand and only the clean water returns to the pool. Over time, more and more dirt accumulates in the filter, reducing the water flow and increasing the filter pressure.

Initially, the dirt in the filter actually benefits the filter performance because the impurities get caught on the sand grains, increasing their surface area. As a result, even more foreign particles get caught in the filter sand.

Over time, however, the filter pressure continues to increase and the filtration performance decreases. When the filter pressure reaches a certain level, then you need to clean the filter system to remove the impurities. By cleaning the sand filter system, we mean you need to backwash the sand filter system.

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When and how often do you need to backwash a sand filter system?

There is no hard and fast rule as to when you need to clean your sand filter system. Instead, you need to check the pool and filter regularly to see when cleaning is needed.

Dirt and debris in the pool will cause the water flow rate to be lower and the pressure to increase. If the pressure rises to a level that is 10 psi (~ 1 bar) above the pressure immediately after the last backwash, you should backwash the sand filter.

Many sand filter systems also have two pressure gauges: An inlet gauge and an outlet gauge. The difference between the two readings, can also be used to determine if backwashing is necessary. Normally, the pressure difference is less than 5 psi. Cleaning is required, however, when there is 15 to 20 psi between the two readings.

Cleaning can also be performed before these pressure levels are reached. The sand filter may already be so dirty before then that the pool water turns cloudy or milky. If you are dealing with cloudy water, the sand filter could be the cause and a backwash is a good idea accordingly.

To keep filtration performance at a high level, you need to backwash regularly. Over time, however, the sand grains rub off more and more, which means that less dirt gets caught in the filter sand over the years. For this reason, you need to replace the filter sand after about three to five years (depending on the particular type of filter sand).

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What causes sand filter clogging?

The most common contaminants that cause sand filter clogging are leaves, algae and dirt particles. During normal pool operation, all of these types of contaminants get into the pool water and into the filter due to circulation. However, there are other contaminants that clog the sand filter.

The pollution of the pool water by the bathers themselves should also not be neglected. For example, if you are hosting a large pool party, the load of skin cells, hair, and remnants of makeup and cosmetics from the additional bathers may require earlier backwashing of the sand filter.

In a new pool, the plaster may rub off quickly. The plaster quickly accumulates in the filter. As a recent pool owner, the cycle between cleanings of your new pool is correspondingly shorter. In practice, however, shows that algae in the pool or other impurities are among the most common causes.

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Backwashing a sand filter system (step-by-step guide).

Backwashing a sand filter is not difficult. Backwashing is simply reversing the water flow of the filter. This flushes the contaminants out of the filter sand. The dirty wastewater is simply disposed of.

Step 1: Turn off the pump

Before you adjust anything on the filter system valves, you must turn off the filter pump. It is best to flip the power switch on the pump as well.

Note: The sand filtration system valve has the following settings:

  • Closed: No water can close. All connections are closed. Do not turn on the pump in this setting.
  • Drain: The filter pump draws in the water and sends it to the drain valve. With this setting, drain the pool.
  • Filter: In normal operation, a pool pump runs on “Filter”. The pump sucks the water and pushes it into the sand filter where it is cleaned. It is then directed back into the swimming pool.
  • Circulate: The pool water is sucked in by the filter pump, but is sent directly back into the pool without being cleaned. You can use this mode to mix the water. This can be helpful if you want to distribute pool chemicals or ensure an equal water temperature.
  • Backwash: The water is pumped backwards through the filter. In this way, contaminants are flushed from the filter sand. The dirty water is then directed to the wastewater valve.
  • Backwashing: Sand grains are stirred up during backwashing. By backwashing, you ensure that the sand grains and dirt residues settle again. The water is also directed to the wastewater valve during backwashing.

Step 2: Set the valve to “Backwash”

At the moment, the filter pump valve is probably set to “Filter”. Starting from this normal mode, you must now set the filter valve to “backwash”.

Step 3: Connect the waste water hose

Connect the garden hose for the wastewater to the drain valve of the sand filter system and lay out the wastewater hose so that the wastewater is flushed to the desired location. Open the wastewater valve for this purpose.

Step 4: Switch on the pump

Start the unit and let the pool pump run for at least 2 minutes. You can check the water flowing through the window on the top of the filter unit. The pool water should change from cloudy to clear over the course of these two minutes. Now turn off the pump and flip the power switch again.

Step 5: Rinse

Now set the valve to “rinse”. During backwashing, the filter sand is stirred up and must first settle again. In addition, the water and dirt residues left behind during backwashing of the sand filter must first be flushed out of the filter before normal operation can be resumed.

The drain valve is also open for this purpose, so that the water does not flow back into the pool. Now turn the pump back on and allow the filter pump to rinse for a minute or two.

Step 6: Filter

Turn the pump off again and set the valve back to “Filter”. Restart the pump and now check the filter pressure gauge. Make a note of the reading to determine when it is time for the next backwash.

Further questions

Why is it necessary to backwash a sand filter system?

If a sand filter system is not regularly backwashed, the filter performance will decrease in the long run. This is caused by the filtered dirt that accumulates over time.

How often do you need to backwash a sand filter system?

The sand filter system should be backwashed regularly. There is no exact time as to how often rewinding is required.

Do I need special tools to backwash?

Neither manual skills nor special tools are needed to backwash a sand filter system.


Sand filter systems are the right choice for the vast majority of swimming pools. The maintenance of sand filter is low, but you need to clean the sand filter system from time to time. Sand filter maintenance is a more important part of pool maintenance and should definitely not be neglected.

For clear pool water, you need to take a look at the sand filter pressure gauge every few days. If the pressure is too high, it’s time for a backwash. A clean filter is the output for a clean pool and will ensure that you maintain the best possible water quality. After all, with these instructions, it’s easy to do.

With that in mind, we hope you enjoy swimming in crystal clear water!

Larry has been a true water rat since childhood. Pure pleasure turned into a passion. That's why he is the first point of contact for friends and acquaintances when it comes to pool-related problems. He is an integral part of the PoolHandbook editorial team.