How To Clean And Backwash A Sand Pool Filter (The Right Way)



There’s different types of pool filters you can use to clean your swimming pool, with sand filters being the most popular due to their reasonable cost and ease of use.

With long hours of circulation required to keep pool water sanitized, filters get a pretty good workout every day.

After so much use, debris builds up in the tank and you’ll need a clean sand filter once again if you want your pool to stay sparkly.

Why Clean Your Sand Filter?

Swimming pools need a chemical sanitizer to kill off pollutants like bacteria, viruses, and various various debris in the water. This is usually chlorine, but some pools use bromine, while others use salt.

Besides that, however, the water needs to be filtered from all the matter left behind – and this is where the sand filter comes in, removing anything as small as 20 microns in your pool water.

Most pools run their system, circulating water and filtering out pollutants for roughly 8 hours a day. As runtime compounds, so does the amount of debris the sand filter purifies.

Sand filters become more effective the longer they work. This is due to the small size of the sand. As pollutants are caught and start plugging holes between sand grains, they begin to block subsequent pollutants from passing through.

With that being said, there will come a point where there’s too many pollutants in the filter, which is when you’ll need to clean your filter out.

Sand filters have a pressure gauge on them that requires monitoring. Once it hits 8 to 10 PSI over the measurement taken when the filter was clean, you’ll have to reduce the pressure by cleaning the filter.

With regular cleaning, a sand filter can last anywhere from 15 to 25 years, and sand only needs to be replaced every 3 to 5 years.

How To Clean Your Sand Filter

There are two ways to clean your sand filter: through backwashing, or deep cleaning.

Backwashing involves reversing the flow of water through your filter to flush it out, and is the most common method. It should be done fairly regularly  (usually weekly) according to your maintenance schedule.

A deep clean is done once a year using a sand filter cleaning solution.

What you’ll need before starting:

  • Backwash hose
  • Multiport valve
  • Sand filter cleaning solution

Step 1. Turn Off Your Pool Pump

Any time you’re performing maintenance on your sand filter, you need to start by turning off the pool pump.

This prevents damage from occurring to the plumbing as well as the multiport valve. Also, take note of the PSI level on the filter’s pressure gauge, which should be 8 to 10 PSI higher than it’s “normal” PSI level.

Step 2. Set The Valve To “Backwash”

The multiport valve on your filter controls how water flows through your pool system. 

Normally, it’s set to “Filter”. This directs water from the pool pump, through the filter, out its “Return” port, and back into the pool. But when backwashing, the valve position needs to be changed.

After ensuring the pump is off, move the valve into the “Backwash” position. This reverses the flow of water inside the filter. 

Normally, water enters a sand filter at the top of the unit, and exits out the bottom. When backwashing, water enters through the bottom, and is reversed to come out the top. 

Also, in the “Backwash” position, water is sent out of the filter’s “Waste” port, so that it doesn’t send dirty water into the pool.

Step 3. Attach Your Backwash Hose

Some pools are designed with a waste line incorporated into them. This makes it simple for waste water to be flushed out and disposed of.

But for the majority of pools, they won’t have a waste line. Instead, you’ll have to hook up a backwash hose to the “Waste” port on your filter.

Backwash hoses are inexpensive and come in either vinyl or heavy duty rubber. We recommend the heavy duty version, as it stands up better to water chemicals, waste, and sunlight, increasing its longevity.

Hoses come in multiple lengths to ensure you can run your waste water to an appropriate drainage point such as a sewer or storm drain.

Also, you should double check your town’s ordinances to find out the proper way to dispose of pool waste water, as some cities have more stringent rules.

Step 4. Backwash The Filter

Turn the pump back on and run it for around 3 to 5 minutes, which will start backwashing the sand filter.

Monitor the sight glass on the side of the multiport valve during this time. Once the water changes from cloudy to clear, shut off the pump once again.

Step 5. Set The Valve to “Rinse”

With the pool pump off, switch the multiport valve’s position from “Backwash” to “Rinse”. 

Rinsing the filter is needed because the sand gets moved around during backwashing and needs to be reset.

Additionally, the filter tank still has backwash and sand sediment in it that needs to be removed so it’s not returned to the pool.

Step 6. Finishing Touches

After you’ve set the valve to “Rinse”, turn the pump back on, and rinse the tank for 30 to 60 seconds.

Once finished, turn off the pump one more time and put the multiport valve back into the “Filter” position.

Turn the pool pump back on to begin normal filtration of the pool once again. Don’t forget to check the pressure gauge, making sure it’s dropped 8 to 10 PSI from when you started the backwash process.

Yearly Deep Clean

Backwashing the filter will be part of your regular maintenance, but once a year you should do a deep clean using a sand filter cleaning solution.

Here are the steps to follow for a deep clean:

  1. Check that your filter’s pressure gauge is 8 to 10 PSI higher than its starting point
  2. With your backwash hose connected, turn off the pump, and move the valve to the “Backwash” position
  3. Turn on the pump and backwash the filter for 3-5 minutes
  4. Turn off the pump, and move the valve back to the “Filter” position
  5. Open the pump lid, and pour the sand filter cleaner into the pump’s strainer basket. For correct dosage, follow the instructions on the bottle.
  6. Turn the pump back on and shut it down after 15 seconds. This moves the cleaner into the filtration tank.
  7. Let the cleaner work its magic in the tank for a minimum of 8 hours
  8. Move the valve back to “Backwash”, turn on the pump and run it again for 3 to 5 minutes to remove debris that the cleaner dislodged
  9. Turn off the pump and move the valve into the “Rinse” position
  10. Turn the pump back on for 15 seconds to rinse out the tank
  11. Turn the pump off and move the valve into the “Filter” position
  12. Turn the pump back on and run your pool system as normal. Be sure to check the filter’s PSI level has dropped 8 to 10 PSI.

Mr. Sandman, Bring Me A Clean!

Keeping a clean sand filter isn’t a difficult job. All it requires is that you follow the proper procedural steps and clean it on a regular schedule. 

This will ensure your pool water always stays fresh and clean, so you can enjoy your pool with minimal headaches.

Categories: Pool Care, Pool Maintenance