How to Backwash a Pool Filter The Smart Way

The backwashing of the sand filter system must take place at regular intervals so that the system filters the pool water. But how is the sand filter system backwashed, and what should you watch out for?

A sand filter system must be backwashed at a pressure of 1.3 kg/cm². To do this, the lever on the multivalve is set to backwash until the water in the system’s sight glass becomes clear. Finally, there is a short rinse so that the dirt does not end up in the pool.

Here you will find detailed instructions on how to backwash your sand filter system. You will also learn when backwashing is necessary, what to look out for and how to avoid problems with backwashing.

Instructions: How to backwash pool filter

Backwashing the sand filter system is essential if the filter pressure is high (from 1 kg/cm²) and if the filter is cloudy.

With backwashing, the system continues to run free from malfunctions, and the pool water remains clean.

But how does the backwashing of the sand filter system work?

Whether your sand filter system is from Intex, Deuba, or other brands doesn’t matter. The process is the same for all sand filter systems – other filters are described below in the text.

You must stick to the exact procedure. If you shift from the instructions, you may have problems with the sand filter, and the process has to be repeated.

1. Switch off the pool pump

First, for your own safety, the operating switch of the pool pump must be set to zero before you adjust the multivalve of the sand filter system and start the actual backwashing.

2. Set the lever to backwash

The lever of the sand filter system is probably set to filter.

After you have switched off the pool pump, you can now move the lever on the multivalve to Backwash (Flush) at 06:00 position.

Backwashing is the necessary position to clean the sand in the filter.

The water is pressed through the filter – against the normal flow direction – and flows off together with the accumulated dirt.

This is where the term backwashing a pool filter comes from.

Tip: Connect a sufficiently long waste water hose to the drainage valve of the filter system. With the hose, you can move the drain to a suitable place in the garden.

3. Switch the pool pump on again

When you have made the correct position of the lever on the multivalve, you can switch the pool pump on again.

You don’t need to do any more than watching the dirty water discharge through the sight glass on the multivalve.

How much pool water is lost during backwashing cannot be determined. The system must run until the cloudy water in the sight glass is clear again.

Then set the operating switch of the pump to zero again because backwashing of the pool filter has not yet been completed, and rinsing must be carried out.

Tip: If later the filter is closed at short intervals, the rinsing was not running long enough.

4. Rinsing the pool filter system

The sand filter system has been backwashed, and a rinse must now be done.

This step is essential, as otherwise, the dirt will get into the pool via the return line.

Did you switch off the pump again after backwashing, as mentioned in step 3? Great!

Now the lever on the multivalve must be set to the 10:00 o’clock position to rinse.

Then turn the pump on again and watch the sight glass again until the water is clear.

Avoid time constraints when rinsing the sand filter system, as they are often mentioned in forums. The process is only complete when the water flows crystal clear through the sight glass.

Note: After backwashing, the filter must always be rinsed.

5. Set the multivalve to filter again

The sand filter system has now been completely backwashed and rinsed. 

You have to switch off the pump again and adjust the multivalve one last time.

To do this, move the lever of the multivalve back to the filter position at 12:00 o’clock.

Done! You successfully backwashed your pool filter.

6. Return to normal operation

In the last step, return to normal operation by setting the operating switch for the pump to automatic mode.

Take another look over your shoulder and check whether the lever of the multivalve is pointing to filters (nose points to the filter).

All the work on the pool filter is now complete.

Why do you have to backwash and rinse the sand filter system?

The standard sand filter in private swimming pools is the most common and provides filtration up to 15 microns (µ).

If you also use a flocculant in the pool, the filter catches even more fine dirt.

That’s a good thing, but as you can imagine, a lot of the dirt remains in the filter.

Initially, the collected dirt supports the filtration of the pool water. But later, the pressure in the filter increases, the return flow becomes weak, and the filter performance decreases significantly.

As a result of poor filter performance, the pool water becomes cloudy.

To prevent the water from becoming cloudy due to the sand filter system, the pool filter is backwashed and then always rinsed.

But what does backwashing mean in the pool filter system?

Backwashing lowers the filter’s pressure and cleans the sand – for better filtration.

The remarkable thing about backwashing is that you don’t have to get your hands dirty.

The sand stays in the filter and is cleaned by the water flowing in – you can find out how to do this above.

This process is repeated at regular intervals so that the water remains crystal clear.

Another advantage of regular backwashing of the pool filter is the water exchange, which lowers the cyanuric acid level in the pool. You can read more about this topic under the link.

How are other filter systems backwashed?

You now know how backwashing works in a sand filter system and how often this should happen.

But what does the process look like with other filter systems for the pool?

  • Cartridge filter: The cartridge filter consists of a grid representing the filter medium. So you don’t need sand or any other filter medium. The cartridge must be removed and rinsed with water from the garden hose. According to the manufacturer’s instructions, fats and oils are removed from the cartridge filter using a special agent.
  • Multi-layer filter system: The multi-layer filter system uses sand and activated carbonate to filter the pool. This is also backwashed as usual, but the activated carbon has to be refilled because it is used up during backwashing.
  • DE filter (Diatomaceous Earth Filter): The DE filter contains DE earth, which is also cleaned by backwashing. Unfortunately, a lot of the filter medium is lost, and you need to replace it. Another problem is that the grid sticks together with grease and oils and must be cleaned by hand.

What causes clogging of the pool filter system?

If the pressure in the sand filter system is high (display is in the red area), then it is clogged.

The reason for this is the dirt retained during the filtration.

But what dirt is causing the blockage in the sand filter system?

  • Foliage and needle leaves: Many leaves and needle leaves end up in the pool, which ends up in the sand filter during filtration unless they have been fished out beforehand with a net. Organic dirt is a coarse contaminant that can clog a sand filter system and pool pump.
  • Algae residues: The algae growth in the pool can hardly be prevented, and with a daily pool pump running time of 6 to 8 hours/day, many different algae end up in the sand filter. You don’t need to worry about green algae. It only becomes problematic if black algae nestle in the filter.
  • Calcification of the sand: Yes, limescale can also cause the sand filter system to clog. If the backwash was unsuccessful, calcified sand is almost always expected.
  • Colloidal substances: During the use of a flocculant, the finest particles are combined into large flakes and thus made filterable for the sand. These include sweat, major dandruff, urine, makeup, sunscreens, perfumes, and much more. All of these substances can clog the filter over time. Therefore, all users should always shower off before swimming in the pool.

With a solar shower in your garden, the time window until the next backwash can be extended by almost 1/3 – provided that most users use the shower.

This is beneficial so that the sand is less worn out and lasts longer.

Tip: A powerful pool pump with a sufficiently large filter basket minimizes the risk of clogging by leaves and other impurities. You can read more about pumps for the pool under the link.

In the case of a sand filter system, the blockage can be cleared quickly and easily using the instructions for backwashing described above.

Much more stressful is to clear a DE filter, which you often have to clean by hand because most of the dirt remains inside.

That leads us to the following question: How often and when do you have to backwash the sand filter system so that it does not clog?

Read more about the right backwashing time in the following chapter.

When and how often should you backwash a pool filter?

Regular flushing of the sand filter system prevents the filter medium from clogging and ensures clear water in the pool.

But what exactly is meant by regular backwashing, and when should that be exactly?

In many forums, it is often claimed that the filter has to be backwashed weekly to improve the filter performance.

But that’s not true.

The filter should not be rinsed as often. Filtration will even improve to a certain point if the filter is not rinsed weekly.

The reason for the improved filtration is that the sand is clogged with the filtered material and can thus better hold back other dirt.

The filter only has to be backwashed at a pressure of 1.3 kg/cm² – the optimal pressure in the sand filter system is below 1 kg/cm².

Another indication that it is time to backwash the pool filter is a weak return, whereby a weak water return can also indicate calcification of the filter sand.

I recommend reading the operating instructions for your sand filter system. The instructions should state how often the backwash should take place.

Tip: The filter should not be backwashed for 9 to 14 days when using a flocculant. This also applies to the use of the algicide based on copper sulfate.

Backwashing would mean that the used chemicals would lose a large part of their effectiveness.

After about 3 to 5 years, even backwashing does not bring the desired clear effect to the pool water.

Then the sand in the filter has to be changed, and the sand filter system cleaned – you can find out exactly how to do this in my other blog post under the link.

FAQ about backwashing the sand filter

Despite the detailed article with instructions for backwashing the sand filter system, some readers have contacted me with specific questions on the subject.

These questions were collected and answered here publicly for all other readers in order to clear up any ambiguities.

Is it essential to flush the sand filter system?

The flushing process of the sand filter system is essential when it comes to keeping the pool water permanently clean.

The process also reduces the pressure in the sand filter system.

The system should therefore be flushed regularly.

Do you need a specialist to flush the sand filter system?

You don’t need to hire a specialist because you want to flush the sand filter system.

The whole thing can be done in a few minutes with my instructions described above.

The specialist will, of course, have a little more experience as to how long the flushing should take. But with the information given here, you will quickly find out how much water needs to be flushed out of the pool.

If you are desperate about the project and your water is cloudy despite good pool hygiene and backwashing, then you have simply failed to use a flocculant.

Which valve settings play a role when backwashing the sand filter system?

Various positions are possible on the multivalve of the sand filter system.

However, for the backwashing of the sand filter system, only the backwash position on the 06:00 o’clock position and the post-rinse on the 10:00 o’clock position are essential.

After the backwashing process, the filter system is set to the “Filter” position as usual.

What to do if the backwashing of the sand filter system does not work?

If the backwash does not work, then the sand may be calcified.

You can quickly check this by opening the lid and manually checking whether the sand has hardened.

If that is the case, then this must be changed.

The best thing to do is to read the article about calcium in the pool to avoid the problem in the future.

Where do you backwash the water by the pool?

Small amounts from the pool can be drained into your own garden.

However, if the water contains additives such as antifreeze or copper sulfate-based agents, it is best not to use them to water the flowers.

Under no circumstances should the water be discharged from the pool into local waters.

What to do if sand comes out when the sand filter is backwashed?

If there is sand in the pool during backwashing, a line in the filter housing has probably broken. 

This has to be replaced before the system can continue running.

Don’t worry. Almost all parts of the filter system can be replaced individually.

However, it can also be that the inlet pipe is broken if it was tightened too tightly during assembly. Here, the part must be replaced too.

Do you have any further questions about the sand filter system?

Contact me at @contactswimfool on Twitter, Facebook, YouTube, or Pinterest – I’ll be happy to help.

Have fun backwashing your pool filter.

Photo of author
Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

Keep Reading