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Thread: Sand filter...is this normal?

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    Sand filter...is this normal?

    I just put an Intex sand filter om my pool a few days ago and after running it awhile during SLAM I'd go out and find my pressure gauge had risen some and flow had slowed way down to almost nothing so I'd backwash and all would be normal again. It just seemed like I was having to backwash a lot. Now I'm noticing that when I go out there and find my gauge up and the flow diminished way down, that I can turn the pump off and not do anything but wait a minute or two and then when I turn it on again, flow seems normal..... What gives?
    18ft. diameter, 48 inch deep Sharkline Reprieve AGP, 7000 gallons, Intex 14 inch sand filter with 3/4 H.P. 2,150 GPH pump, Intex SWG
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    Mod Squad pooldv's Avatar
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    Re: Sand filter...is this normal?

    It is normal if you have early stages of algae growing in your pool. Got any water test results? Any history over the last few days of higher than normal chlorine consumption? Is your pool cloudy, green or slimy on the sidewalls?
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    Re: Sand filter...is this normal?

    Pool is light green and I can see bottom well enough to have scooped all leaves out. I started a SLAM just the other day and posted some of the readings elsewhere. I expected having to backwash while doing the SLAM. Have a CYA reading of 30 and have been testing and trying to keep the shock level at 12 for FC. My concern is more that the flow will slow to almost nothing and then just simply switching off the pump, waiting a minute, and switching it back on seems to restore flow. No backwash is necessary. The same thing will happen a little later and I can do it again. Just wondering if there is some fault with my new filter or my setup because being able to re-establish flow like that seems strange. Of course I have been back washing every once in awhile just because I think I need to. BTW...SWG in my sig has not been put back inline yet. Trying to get everything else sorted out first.
    18ft. diameter, 48 inch deep Sharkline Reprieve AGP, 7000 gallons, Intex 14 inch sand filter with 3/4 H.P. 2,150 GPH pump, Intex SWG
    TF-100 test kit

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    Re: Sand filter...is this normal?

    My concern is more that the flow will slow to almost nothing and then just simply switching off the pump, waiting a minute, and switching it back on seems to restore flow.
    Here's what's happening.......When the flow slows, your filter is clogging with a layer of dirt mostly on the top of the sand bed. When you turn of the pump, that sudden loss of pressure and flow jars that fine layer dislodging it (but not removing it)

    Then, when the pump is started back up, that restricting layer has been disturbed which allows your filter to return (temporarily) to it's normal flow.

    You should completely disregard it. When your psi rises 25% above normal, you should backwash correctly, rinse, and then turn the filter back on. That immediate lowering of your psi is a false sense that you are cleaning the filter.......you are not. You are only dislodging the layer of dirt temporarily.......a complete backwash is needed to remove it from the filter.
    Dave S.
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    Re: Sand filter...is this normal?

    Quote Originally Posted by duraleigh View Post
    Here's what's happening.......When the flow slows, your filter is clogging with a layer of dirt mostly on the top of the sand bed. When you turn of the pump, that sudden loss of pressure and flow jars that fine layer dislodging it (but not removing it)

    Then, when the pump is started back up, that restricting layer has been disturbed which allows your filter to return (temporarily) to it's normal flow.

    You should completely disregard it. When your psi rises 25% above normal, you should backwash correctly, rinse, and then turn the filter back on. That immediate lowering of your psi is a false sense that you are cleaning the filter.......you are not. You are only dislodging the layer of dirt temporarily.......a complete backwash is needed to remove it from the filter.
    Thank you for the concise answer. I was puzzled. I have been doing the backwash as you described but sort of accidently discovered the other phenomenon and was worried it was an issue. Glad it's not. I just did my last chlorine test for the evening and seemed to have maintained my shock level since the earlier one today. Pool is still light green clear and it's hard to see progress but I only started a couple of days ago. Problem is that heavy rains are forecast beginning tonight and all day tomorrow so I wonder what that's going to do. Perhaps I should just set the pump to recirculate and bypass the filter overnight.
    18ft. diameter, 48 inch deep Sharkline Reprieve AGP, 7000 gallons, Intex 14 inch sand filter with 3/4 H.P. 2,150 GPH pump, Intex SWG
    TF-100 test kit

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    Mod Squad tim5055's Avatar
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    Re: Sand filter...is this normal?

    Quote Originally Posted by Noah_Count View Post
    Problem is that heavy rains are forecast beginning tonight and all day tomorrow so I wonder what that's going to do. Perhaps I should just set the pump to recirculate and bypass the filter overnight.
    If you are not going to be checking the filter for hours (like when you are sleeping) then yes, recirculate if you feel there is a chance of it clogging.

    Algae grows in the rain and you can kill it in the rain, just wear a rain coat. Test & adjust your SLAM FC during rain the same as on a clear day. The more often you test and adjust the easier & quicker a SLAM will progress.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Sand filter...is this normal?

    Quote Originally Posted by tim5055 View Post
    If you are not going to be checking the filter for hours (like when you are sleeping) then yes, recirculate if you feel there is a chance of it clogging.

    Algae grows in the rain and you can kill it in the rain, just wear a rain coat. Test & adjust your SLAM FC during rain the same as on a clear day. The more often you test and adjust the easier & quicker a SLAM will progress.
    Yes, I just decided to go ahead and set it to recirculate for the night. Pressure gauge reading looked good but I feel safer with it on recirculate. I will definitely be testing when the rain allows tomorrow even though the forecast calls for periods of heavy downpours. Every reasonable chance I get, I'll be out there working on it.
    18ft. diameter, 48 inch deep Sharkline Reprieve AGP, 7000 gallons, Intex 14 inch sand filter with 3/4 H.P. 2,150 GPH pump, Intex SWG
    TF-100 test kit

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