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Thread: Backwash and Filter PSI question

  1. Back To Top    #1
    Bigdog43's Avatar
    Join Date
    Jul 2016
    Memphis, TN

    Backwash and Filter PSI question

    I am a brand new pool owner going on 7 days now. The previous owner had a pool guy that I will continue to use until I get my arms around everything. I'm a DIY'er so I'll eventually do all this myself...or that's the plan. (I have yet to get a hold of the "pool guy")

    I'll tell you what I know about it. It's a low chlorine, in ground pool with a waterfall in the deep end. I think it's 35k gallons. I have a sand filter and my climate is outside of Memphis TN. I have not had the water tested yet and the water is clear.

    The previous owner gave me a crash course on what he does as far as maintenance.

    -Drop a couple of chlorine tablets in the skimmer each week
    -Backwash every so often
    -Empty skimmer and polaris debris bag as needed
    -Clean out pump skimmer each week or so

    Here's my question: The gauge on the filter has never been lower than say around 18 since I've been looking at it. Almost every day of the last week, I've watched this gauge and it creeps up to the mid 30's and the water feature slows to a trickle. So on the first day, I backwashed, rinsed and cleaned all skimmers. When I turned everything back on, the water feature was rocking and rolling and all was good...except the same thing happened the next day, etc. After a backwash/rinse, the gauge goes back to around 17-18 and then slowly creeps up.

    I know this is too often to backwash, but I don't know what else to do. Is this increase in PSI normal? Is mid 30s to high? I'm thinking the sand in my filter needs some attention. Can someone help?

    PS: Some additional info is that I feel certain me and my family (and dogs) have used this pool more in the last week than the previous owners probably did in a month. We've also had two really big storms in this week.

  2. Back To Top    #2
    Mod Squad
    Join Date
    Aug 2012
    DFW, TX

    Re: Backwash and Filter PSI question

    Welcome to TFP!

    We recommend backwashing your filter when the pressure rises 20-25% above clean pressure.

    The reason it is clogging so fast is because you have algae growing in the pool. The reason there is algae growing in the pool is because there is not enough chlorine. Chlorine must be maintained above minimum for your CYA at all times, FC/CYA Chart, to keep the pool sanitary and algae free.

    You can do an Overnight Chlorine Loss Test to verify that there is algae growing. If there is then SLAM the pool to kill the algae.

    You will need a good test kit to do these things. I use the TF-100 test kit and I buy mine at

    To learn more about water chemistry start here
    ABCs of Pool Water Chemistry and here, Pool School - Getting Started
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  3. Back To Top    #3
    Bigdog43's Avatar
    Join Date
    Jul 2016
    Memphis, TN

    Re: Backwash and Filter PSI question

    Thank you so much for the reply Here's an update on my situation. I may have been a little dramatic on my original post. I had backwashed the day of that post and it stabilized and the filter gauge has stayed right around 18-20 ever since.

    Talked to the pool guy, couple things:

    -He suggested that maybe I wasn't backwashing for long enough and it wasn't doing what it needed to do, which allowed the pressure to keep creeping up. And that maybe that last backwash did it. Another thing is that there is no sight glass on my system, so I can't backwash until the water is clear, so it's going to be hard to know how long I need to do it. He recommended doing it for like 5 minutes.

    -Secondly, he replaced the gauge on my filter because even when the pump was off, it was reading 10PSI. He backwashed and now the new gauge is reading under 15.

    -He also said i'm not putting enough clorine tabs in. I'm learning that the owner wasn't as involved as he said he was and he didn't know exactly what was needed to keep the pool healthy.

    I will order the test kit and start reading about the chemistry. Thanks!
    Memphis, TN.
    Pool IG, 20K gallon, Gunite. Triton Sand filter, Chlorinating Liquid, Rock Water Feature, New plaster 2015
    Spa 450 gal, Tropic Seas Waikiki 864L, Bromine
    Taylor K-2006

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