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Thread: When to replace cartridge filter

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    robdac's Avatar
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    When to replace cartridge filter

    With my pump setup the pressure on the gauge doesn't rise enough normally to tell when the filter is dirty and needs to be cleaned. Normal pressure on my variable speed rig at 1500 rpm is 6psi. When I crank the pump up on a clean filter the system pressure is around 16psi and not much higher (17 psi) on what I'd consider to be a fairly dirty filter after a month of service. I have two identical filters and just swap them each month for convenience. After swapping them, I clean the dirty filter with a hose, let it air dry, then put it away for the next swap. Sound about right?

    Also, how do you folks determine when it's time to time to actually replace the filter rather than just clean it up? Physically, my filters both still look good. If they were torn or had bands coming off it would be obvious that it's time to replace. Are there any other indications?
    11K gal IG screened-in plaster pool w/ spa
    pentair 150 cartridge filter, Pentair Intelliflow VS pump,
    Aquarite AQR15 SWG, AquaCal Heatwave Heat Pump, TF-100 test kit

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    Texas Splash's Avatar
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    Re: When to replace cartridge filter

    Typically we advise to clean filters when the pressure increases by about 25%. But like you, my simple gauge and single cartridge filter doesn't really increase that much when dirty. Later I may try the more precise glycerin-filled gauge on the TFtestkit web site. But for now, you have the right idea with cleaning. Swapping filters is great during cleaning, and replacement once a filter is starting to fall apart is what I do as well.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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    duraleigh's Avatar
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    Re: When to replace cartridge filter

    You are both discussing what seems to be a reasonably common condition........A cartridge filter may not give you the 25% you are looking for as a signal to backwash.

    While my experience has been only with sand, it seems to me that the cartridge is simply not yet near it's capacity and there is no reason to change it out. The psi is a measurement of resistance and if your filter is not resisting by 25% or more (than it was when clean) there is really no reason to clean it.

    If I recall, mas985 (our real authority on this subject) has a cartridge filter system that can go virtually all season without being backwashed. In short, his pool stays very clean and it sounds like yours does the same.

    Since you don't get the 25% increase, what does the cartridge look like when you pull it? Really dirty? Not so much?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    robdac's Avatar
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    Re: When to replace cartridge filter

    When I exchange the cartridges they certainly don't look clean but they don't look filthy either. I haven't been doing it nearly as long as some folks here. Usually when I exchange them I'm glad that I did it given the condition (dirtiness) of the filter. That said, I may not know what a really dirty one looks like. When I spray it off with the hose it's pretty obvious that it was dirty however.
    11K gal IG screened-in plaster pool w/ spa
    pentair 150 cartridge filter, Pentair Intelliflow VS pump,
    Aquarite AQR15 SWG, AquaCal Heatwave Heat Pump, TF-100 test kit

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