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Thread: Does CYA ever dissipate over time?

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    Does CYA ever dissipate over time or is the only way of lowering it done by splashout or water replacement?

    Craig
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    JasonLion's Avatar
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    Yes, but normally only over the winter. There is some process, no one is sure quite what but probably anaerobic bacteria, that can remove most or all of the CYA over the winter. This seems to happen about 1/3 of the time and is usually associated with covered pools that get algae over the winter.

    The other thing that happens is that people often underestimate how much water replacement can happen from rain and splash out.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    ivyleager's Avatar
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    Quote Originally Posted by 257WbyMag
    Does CYA ever dissipate over time or is the only way of lowering it done by splashout or water replacement?

    Craig
    Yes, mine went from 100ppm to 35 over the winter, and I DID NOT have any algae problems. Testing with Ben's Pool Kit.
    CaryB
    36 x 18 IG vinyl, 25K, 1 HP pump, sand filter
    1 skimmer, 2 returns, no main drain
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    ivyleager,

    Did your chlorine level get towards zero over the winter or were you maintaining its level? If it went to zero, the soil bacteria could then grow in the pool consuming the CYA, and when you opened up you'd have a lot of ammonia in the pool (the bacteria break down the CYA into ammonia and carbon dioxide). So you might find a HUGE chlorine demand upon startup as you have to oxidize all the ammonia.

    If you maintained FC levels over the winter, then the drop in CYA is more of a mystery.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Well, gee, I wish mine would do the mysterious winter drop! I've been working on lowering mine for the past 2 years. When I bought the place it was at 122, so have had 2 full summers using strictly BBB method (thank you guys!!!! I learned everything about pool care from the message boards!) along with Polyquat 60 due to high CYA's. I think I ended last season at about 95. Realizing that our season is only 4 months, if that, being here in Minnesota. Still have aways to go but it will get there. Since it's only me who uses the pool I don't get alot of splash out so rely on rain and backwashing/evaporation/topping off to getting the level down. Eventually it will get there!
    Mona SE MN
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    ivyleager's Avatar
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    Quote Originally Posted by chem geek
    ivyleager,

    Did your chlorine level get towards zero over the winter or were you maintaining its level? If it went to zero, the soil bacteria could then grow in the pool consuming the CYA, and when you opened up you'd have a lot of ammonia in the pool (the bacteria break down the CYA into ammonia and carbon dioxide). So you might find a HUGE chlorine demand upon startup as you have to oxidize all the ammonia.

    If you maintained FC levels over the winter, then the drop in CYA is more of a mystery.

    Richard
    Yes, it was rock bottom of zero when I officially opened last year in April. However, for most of the winter the pool stayed on line, I was able to circulate chemicals (bleach and an occasional 8 oz of Polyquat). It was at zero several times over the winter, tho. Just added bleach when needed, which wasn't too often. I did have a 12 hour episode of "cloudy" water in May, which I just shocked and it went away. Early stages of a bloom, I'm sure.
    CaryB
    36 x 18 IG vinyl, 25K, 1 HP pump, sand filter
    1 skimmer, 2 returns, no main drain
    Old school: PoolSolutions test kit

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