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Thread: CYA decreasing over time?

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    Join Date
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    Question CYA decreasing over time?

    I normally maintain my pool with liquid chlorine and muriatic acid. I keep my FC level at the desired percentage of CYA, using the TFP guidelines. Have had no algae problems since I began using this method.

    I have an in-line chlorinator that uses 3" tri-chlor tabs, but I only use it for a few weeks at a time, if I am away and cannot tend to the pool. Last September, after using tabs for a few weeks during my absence, I measured the CYA at 65. Since that time, I have only used liquid chlorine. Today, I measured the CYA at 45. I do not backwash the pool, since I have a cartridge filter.

    Is it possible for CYA to go down that much in 7 months if the only way that water leaves the pool is by evaporation? Allowing for measurement errors, it could have been 60 last September and 50 today, but that is still a noticeable drop. I'm not complaining, because I may have to use tabs again for 3 weeks when I go on vacation soon. Just wondering what can cause CYA to drop, since I see people on this website saying that it can only go down when some of the water is removed by backwashing or draining, not by evaporation.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit; Location: Southern California coastal

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    Mod Squad tim5055's Avatar
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    Re: CYA decreasing over time?

    Yes, entirely possible. As you point out, there is a testing variance to consider and CYA will naturally degrade a few ppm per month, maybe a little more.
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    Re: CYA decreasing over time?

    CYA does reduce over time and a deep end discussion about it is in this thread, Degradation of Cyanuric Acid (CYA).
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
    Hayward Aqua Rite T-15 SWCG, Jandy LXi 400k BTU NG heater, 350 sq.ft. of Sun Star solar panels, TF-100 Test Kit, Dolphin s300i Cleaner
    Test Kits . Pool Math . Chlorine/CYA Chart . The SLAM Process

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    Re: CYA decreasing over time?

    Quote Originally Posted by ping View Post
    CYA does reduce over time and a deep end discussion about it is in this thread, Degradation of Cyanuric Acid (CYA).
    Thanks. Based on my measurements I lost 20 ppm in 7 months, so about 3 ppm per month, which seems reasonable based on the thread. The pool is never covered and FC is always maintained so that there is no algae or bacteria to affect the CYA. I will probably be using the tri-chlor pucks for 3 weeks during an upcoming vacation, so its good to know that my CYA has dropped since the last time i had to do this.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit; Location: Southern California coastal

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    Paul & Crystal's Avatar
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    Re: CYA decreasing over time?

    I am also experiencing a noticeable drop in CYA. I did back wash twice for a couple minutes about 6 weeks ago when I first got the pool. After the backwash I was rounding up to 50. Now 6 weeks later I'm at 40. I've not decided yet how I will bump it up.

    Crystal
    60K 53 X 23 X 3'-10' IG Grecian Concrete aka "The Beast"
    TF100 XL with Speed Stir
    Dolphin M500 aka "The Beast Master"
    Sta Rite Max E Pro 2 HP - Hayward Pro Series Sand Filter S310T.
    My Pool Thread: Old School Pool

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