How to Backwash a Pool Filter – A Fast and Simple Guide

Kevin Pflug

Knowing how to backwash a pool filter is a major factor in keeping your pool crisp, clean, and ready to go. The filter’s primary job is, well, filtering…and this job can’t be done properly unless it is unclogged.

Having a dirty filter is almost always a prime suspect when we are facing pool issues…whether it’s weak water flow, a dirty or cloudy pool, or certain equipment not functioning properly.

Let’s learn how to maintain our filter so that we can keep that nice, crystal-clear water we all desire.

Why Should You Backwash Your Pool Filter?

As your pool filter is doing its’ job, it becomes dirty as various contaminants start to get stuck to the media. As these contaminants start to build up on the cartridges, or grids (if you have a DE filter), it gets harder and harder for the water to circulate.

A blockage of sorts starts to occur…much like how it is harder for blood to pass through our arteries to our hearts as plaque builds. In addition, the pressure in the system starts to increase (much like higher blood pressure).

We don’t want our filters to have a heart attack, and backwashing the filter really helps get rid of all that excess junk. It can help relieve the higher pressure in the filter, and get the water circulating properly again. As backwashing becomes less effective, a full-on filter cleaning will have to be completed.

You can find out how to embark on the journey of a deeper filter cleaning here: deep clean your filter.

Lastly, backwashing a pool is of vital importance because it helps prolong the life of your filter. Replacing cartridges or DE filter grids can be very expensive. The cleaner you keep your cartridges/grids by regularly backwashing, the more life you will get out of your filter media.

How Often Should You Backwash Your Pool?

You should backwash your filter once the PSI on the pressure gauge raises to too high of a level. How high is too high? Well, usually when your baseline PSI level raises to about 10 PSI or more.

In order to know what your baseline PSI is for your filter – be sure to check your pressure gauge after a good filter cleaning, or when your filter is first hooked up.

If you’re unsure of what your baseline level was, or if your pressure gauge is broken, you can default to once or twice a week during the pool season.

If you notice your returns pushing a little weak, or your skimmer suction doesn’t seem great – give backwashing a go after emptying all your baskets. Don’t worry because as you will soon see, backwashing is a fairly simple process!

How to Backwash a Sand Filter in 8 Easy Steps:

  1. Turn off the pool system.
  2. Connect the backwash hose to your waste line if it is not hooked up already.
  3. Put the multiport valve in the “backwash” position.
  4. Turn on the pump and wait till the water running through the sight glass is clear.
  5. Next, turn off the filter system, and put the multiport valve into the “rinse” position.
  6. At this point, turn on the pump again and wait till the water running through the sight glass is clear.
  7. Shut the system off one more time and place the multiport valve back into the “filter” position.
  8. Turn back on the pool pump. You did it!

Backwashing a DE Filter:

  1. Follow steps 1 to 7 above, then:
  2. Make sure the pump is running properly so the DE you’re about to add can circulate through the system.
  3. Add the manufacturer’s recommended amount of DE to the skimmer (a little at a time).

Most of your filtering issues can be solved by following the above guide. It only takes a few minutes and can really make a world of a difference for your pool and your pool system.

If you still have low flow after backwashing your pool filter, then you will most likely have to get down and dirty and give the filter a thorough cleaning.

Even if you now know how to backwash a pool filter…if you don’t want to get involved yourself, please feel free to get in touch with us by texting/calling 631-472-6275 or emailing us at

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Kevin Pflug
Kevin joined Romanelli & Son Pool Service in 2021 and hasn't looked back since! He enjoys eating his wife's delicious homemade meals and bowling with his family.