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Thread: Sand Filter pressure question (rising quickly)

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    Sand Filter pressure question (rising quickly)

    Bought the house and closed at the end of June. Spent a number of weeks battling back mustard algae. Finally got the upper hand on it last week and the pool has been amazingly clear and wonderful ever since. All of my numbers are good as well.

    Now the previous owners didnt do much, if anything, in terms of mechanical and chemical maintenance. So i've been replacing things since we moved in. Seems everything mechanically has been sound and great however i'm having issues with filter pressure. With the onset of the algae, and the constant battling, i've either been vaccuming to waste when the dead algae settled on the bottom, or vaccuming and then backwashing.

    Pressure post backwash is always right around 12-13psi. Flow is never reduced and always super strong out of my returns. No main drain, just two skimmers at opposite end of the pool, always cleaned and maintained. Filter basket always cleaned out as well. So post backwashing, the pressure holds around 12-13psi but within 5-6 hours i'm back up around 17-18psi. After a few days, or after vaccuming any settled debris/waste i will spike somewhere around 20. A backwash will get me down to 12-13psi but it always comes right back up to 17-18psi a few hours later.

    Question remains.......is this normal? Is my normal pressure this high? Flow is never reduced, always super strong and consistent. Filter doesnt sound like its struggling, and as far as i can tell, theres no clogs anywhere.

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    Re: Sand Filter pressure question (rising quickly)

    So post backwashing, the pressure holds around 12-13psi but within 5-6 hours i'm back up around 17-18psi
    Your filter is doing what it is supposed to do....filter debris out of your water.....whether you can see it or not, it is in there and that is causing your psi to rise.

    I suspect you have algae in the pool that you cannot see.

    Posting a full set of test results is the first step towards solving your issue.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Sand Filter pressure question (rising quickly)

    FC-4
    TC-4
    CYA - 30
    ALK - 90
    PH - 7.5

    No hardness test since its vinyl and no heater, no phosphates present.

    Chlorine and CYA has been stable for about a week. When i was having algae issues the chlorine wouldnt hold or would be much lower

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    Charlie_R's Avatar
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    Re: Sand Filter pressure question (rising quickly)

    What test kit are you using?
    15'x48" 4500 gallon Intex pool, buried 1.5 ft. Pac-Fab Dynamo 3/4 hp pump. Hayward S180T sand filter, bought used. Taylor K-2006 test kit. Rocket mass heater based wood fired pool heater.

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    Re: Sand Filter pressure question (rising quickly)

    Your numbers look pretty good and you report crystal clear water so that doesn't seem like an algae issue but it still could be.

    Something is being deposited in your filter, no doubt. I would suggest you backwash anytime you get a 25% rise from your clean pressure so that would be around 16 psi.

    Next, I would raise the FC to up around 6-10 ppm this evening and perform an OCLT. There are instructions on how up in Pool School. That will be a great indicator to see if your pool is algae free.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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