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Thread: 10 PSI over normal before backwash?

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    10 PSI over normal before backwash?

    It is said over & over again not to backwash a sand filter until the pressure is about 10 psi over the normal reading. With mine, at just 4-5 psi over normal, the water doesn't seem to be flowing into the skimmer very well & the water in the skimmer is barely moving & dust, dirt, etc. is floating on top of the water in the skimmer. Is that normal or should I go ahead & backwash?

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    JasonLion's Avatar
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    Re: 10 PSI over normal before backwash?

    Go ahead and backwash if you want. There is no fixed rule about 10 psi over, some people do 6 psi or 8 psi, some people go a week or a month. Do whatever works for you. The main down side to backwashing too frequently is that you lose water every time you backwash.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: 10 PSI over normal before backwash?

    Am I correct in thinking that when the water looks stagnant in my skimmer that it is probably not filtering well even though it still seems to have a good flow out the return?

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    mas985's Avatar
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    Re: 10 PSI over normal before backwash?

    One thing to remember is that 10 PSI is 23 feet of head so if you wait that long, you will be reducing the flow rate of your pump by quite a bit. I would backwash well before 10 PSI and probably before 5 but you have to balance that with how often you would be doing it. A backwash every couple of weeks at 5 PSI is reasonable while every week many not be. There really is no hard and fast rule but I do think 10 PSI is too high.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: 10 PSI over normal before backwash?

    5-10 psi is the general rule for commercial pools, but commercial pool filtration systems are supposed to be sized so they achieve correct turnover *with* a dirty filter. It doesn't always work out that way though.

    I usually recommend backwashing as little as possible but don't exceed 10 psi. If the filter system isn't achieving good flow at a lesser PSI then that's when you need to backwash.

    The main reason is that a sand filter with some dirt load will filter better than a clean filter. Water waste and *possibly* wearing out the sand quicker is also an issue but that last one is somewhat debatable.
    21' Leslies Beachland Ag Pool, 10,000 gallons, professionally installed (best money I ever spent) Hayward 16" sand filter w/Pentair two speed pump Fafco 4x20 solar heater,Aqua Trol RJ. Borates added. Hard plumbed.

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    Re: 10 PSI over normal before backwash?

    Quote Originally Posted by Aquaman95
    The main reason is that a sand filter with some dirt load will filter better than a clean filter.
    Cool, I had heard this before. I usually wait until 10 psi over the starting pressure, but after my BBB conversion early this season, the filter won't go any higher than maybe 4 psi over its' starting point. So before vacation I backwashed, but haven't really had to in weeks since then. Is that normal with new sand?
    Todd
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    Re: 10 PSI over normal before backwash?

    Yes, that can be normal with new or even old sand. Those pressure gauges can get clogged but as long as you see movement out of it and it drops to 0 when you shut the system off the gauge should be fine.
    21' Leslies Beachland Ag Pool, 10,000 gallons, professionally installed (best money I ever spent) Hayward 16" sand filter w/Pentair two speed pump Fafco 4x20 solar heater,Aqua Trol RJ. Borates added. Hard plumbed.

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    Re: 10 PSI over normal before backwash?

    Quote Originally Posted by bassadict69
    Am I correct in thinking that when the water looks stagnant in my skimmer that it is probably not filtering well even though it still seems to have a good flow out the return?
    Check to make sure the weir (floating flap) on your skimmer is present and moving freely. If it is missing or stuck down (not floating), the water in the skimmer will look abnormally still even if the flow is normal.
    Currrent pool under construction: DIY Kafko steel/vinyl IG 26kgal 20x40 Kidney, sand filter, Triac spillover spa, Aqua Logic SWG
    Previous pool: IG vinyl 20x40 rectangle. Made all the mistakes - now reformed (mostly)

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