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How Often Should I Backwash My Filter? How Long?

The Secret to Backwashing Your Filter: Backwash Longer, but Less Often!

Many pool owners backwash weekly as part of their maintenance routine. However, it’s not necessary to backwash that frequently! The ideal time to backwash is when the pressure shown on your filter gauge reaches 8-10 psi (pounds per square inch) higher than your normal running pressure.

This may sound odd, but allowing some dirt to sit in the filter sand actually helps to create rough edges so the sand can catch small debris. Backwashing too often can stir up the sand and allow small particles to pass through the filter and back into the pool.

A sand filter should always be backwashed for a minimum of 3 minutes and a maximum of 5 minutes depending on the size of the filter. Backwash for at least 3 minutes, even if the water leaving the backwash line or the water in the site glass is clear. Sometimes the filter sand will have a clear patch in it where no or very little debris has been trapped. Since the water pushes the debris from the bottom of the filter to the top of the filter, if backwashing is stopped at a clear patch, the debris underneath it forms a barrier in the sand and the filtration can no longer perform at its full potential.
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    What should I do if I have added water chemicals, and backwash the pool and the water is still cloudy?
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  • How long should I backwash without a sight glass to check the water clarity?
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  • Mike Drummond (Dealer Development Manager) June 18, 2013 16:14
    Hi Gregory, a full backwash lasts 3-5 minutes. This should be done regardless of water clarity. Sight glass or not. After that, consider doing a rinse for 30 seconds, then return to the filtration setting.

    If you are experiencing clarity issues, the first step is to bring a water sample to your closest Dazzle retailer. They can run a series of tests to determine what the cause of the clouding may be. In some cases, it can be related to the amount of chlorine in the water, sometimes it is related to particulate in the water (ie. dead algae) and other times it could be from chemistry.

    The retailer can help guide you on the right path to correcting the cloudiness.

    Let me know if we can help further.
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  • How often should I change the sand in my filter? I have owned my home for 5 years and have not changed the sand. Unsure as to how long it had been before I got it.
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  • Mike Drummond (Dealer Development Manager) May 13, 2015 19:32
    Hi Logan, great question! 

    It is tough to say how often sand should be changed in a filter as it is dependent on how well the pool water has been maintained and the quality of fill water.  Most pool retail and service businesses would suggest changing sand every 7 years.  My general rule of thumb when buying a home with a pool, is to change the filter sand sooner rather than later.  Most often, we don't know how the previous owner cared for the pool.  How well was the water balanced in the previous years?  How often did they have problems with algae, scale or metals?  How often did they chemically clean the sand?  If you don't know the answers to those questions, I recommend changing the sand.  Now, if you've had no issue with water clarity or quality, you might be able to get away with simply doing a chemical cleaning of the filter.  Not a bad place to start anyhow.  We have a filter cleaner called Rapid Action Filter Cleanse that will strip any deposit from the sand and break down any grease, grime or other organic matters.  This will render the sand almost new again.  The treatment is relatively simple.  Shut the pump off, put the filter in backwash.  Open the pump lid and turn it on.  Pour the contents of the filter cleaner into the pump basket and count to ten.  Shut off the pump and let it sit for 1hr.  After the hour is complete, backwash the filter for 7 minutes.  This should be adequate to get all of the filter cleaner and the stuff it has released out of the filter completely.  Then go ahead and put the pool back into the filtration mode.

    I hope this helps.  Let me know if you have any questions.
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  • we just opened our pol two days ago and it is clean, but cloudy. should we backwash since this is the 1st time that we have run the system this year?
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  • Mike Drummond (Dealer Development Manager) May 19, 2015 13:41
    Hi Mari,

    Before backwashing the filter, give the pool time to circulate.  Make sure the return jets are aimed downward on a 45 degree angle and aimed away from the skimmer.  Keep the pump running 24hrs/day.  It is also a good idea to make sure the chlorine level in the water is up to 1-3ppm.  Sometimes the clouding can be caused by insufficient sanitizer level.  If after doing this, the pool remains cloudy, consider a filter aid like clarifying tablets.  Once the water is clear, then backwash the filter.

    Let me know if we can assist further. 
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  • I back wash my pool yesterday as the pressure was reading high. Now the pressure is still high but I believe that i did not back wash long enough. Can I do it again? WOuld that help the cloudiness also.
    Thanks
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    • When I backwash the water drains out so I have to add more water it goes under the filters
    • Mike Drummond (Dealer Development Manager) May 10, 2017 17:18
      Hi Jean!  When backwashing, the water should come out the backwash line.  If you are experiencing water coming out of anywhere else, I'd suggest that you contact a pool professional to take a look at the problem.  There are a number of possible causes.  It could be that there is a leak in the filter head or tank, The port valve gasket could be degrading.  The plug in the tank could be broken....A pool service person will be able to ascertain the source of the issue. 

      I hope this helps.  Let us know if we can help further.
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  • I purchased a home with a pool a little over a year ago and don't have a lot of experience with maintaining a pool. I haven't been relying on my filter gauge to determine the need to backwash, I've just been backwashing weekly. However I like what you're saying about doing it less often for a longer period of time based on the reading on my filter gauge. What is the typical normal running pressure so I can determine when it's running 8-10 psi higher than normal?
    • Mike Drummond (Dealer Development Manager) July 20, 2015 15:35
      Hi Susan.  Great question!  There is no 'normal' running pressure.  There are a number of variables that can impact the pressure in the filter.  Size of pump, distance from pool, uphill or downhill suction, amount of sand....I do often see many pools operating between 10-13psi however. 

      When you get your pool started up in the spring, the filter is presumably clean and the pump is properly primed.  At this point, you will be able to note YOUR normal operating pressure.  As you know the pressure builds up when debris is trapped in the filter.  After a good backwash 3-5 minutes, the pressure should return close to that original pressure.

      Please let me know if I can assist further.
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  • I just replaced my hay would sand filter because of age it cracked. So I have new hoses, new sand, new valve, the whole set up. It runs like a new car. I have good pressure no problem My question is over the past couple of days I notice the pressure climb to the backwash level and I backwash no problem and the pressure returns to normal pressure for my pool. Should that pressure be rising like that every other day for me to backwash, mind you when I back wash, the water is cloudy in the glass but then runs clear after 3-4 minutes. I was wondering id new sand had anything to do with it.

    I did put phosphate remover in the pool and chlorine.
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  • Mike Drummond (Dealer Development Manager) May 21, 2019 16:42
    Hi Edwin, great question!

    There are a couple of things to consider here.

    1. New sand will need a bit of time to "pack down". This could lead to filter pressure rising daily until the sand is fully compacted.

    2. By adding a phosphate remover, the filter is trapping orthophosphates. Since the phosphates are held in the filter, it will also contribute to rising filter pressure.

    Keep in mind that once you backwash, the phosphate remover is no longer in the filter and cannot remove phosphates.

    I would suggest that you allow the filter to run for a few days and see if the pressure levels out. Your "new normal" may be different than what you had previously seen. New sand should improve the filtration, but could slow down the rate of water flow, resulting in a higher filter pressure.

    By letting it run for a few days, you should see a levelling off of filter pressure before it starts rising again.

    Keep us posted and let us know if we can help further!
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