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Thread: Not using pucks or a lot of shock but CYA keeps going up

  1. Back To Top    #1

    Join Date
    Oct 2015
    League City, TX

    Not using pucks or a lot of shock but CYA keeps going up

    I don't understand why I'm constantly fighting high CYA after numerous drain and refills, stopped using the chlorine pucks and started using liquid bleach. Shock the pool about every month or two and my CYA still is high (70). I didn't think anything besides the pucks and the shock added CYA. Any help would be appreciated.
    Pool Volume: 15000 gal
    League City, Tx

  2. Back To Top    #2
    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: Not using pucks or a lot of shock but CYA keeps going up

    The CYA test is affected by temperature. So if the water is warmer now than it was the last time you checked the CYA, it could be a better reaction so it reads higher than it did.

    Testing indoors versus outdoors also can make a HUGE difference.

    How much is "not a lot of shock?" According to poolmath, if you use a 1 lb packet of dichlor, that will add 4 CYA to your pool. Given the subjectiveness of the test, just 2 packages could jack the CYA by 10.
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  3. Back To Top    #3

    Re: Not using pucks or a lot of shock but CYA keeps going up

    Do pool or spa water samples have to be at "room temperature" before testing begins?

    With one exception, no. Our lab has run the pH, total alkalinity, calcium hardness, free chlorine, and cyanuric acid tests on known standard solutions at approximately 104F, 75F, 60F, and 40F. Only at 40F did the CYA standard solution test higher than its actual value (after accounting for test variability). All other tests were unaffected by temperature differences.
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  4. Back To Top    #4

    Join Date
    Aug 2012
    Houston, TX

    Re: Not using pucks or a lot of shock but CYA keeps going up

    I would concur that you answered your own question when you stated you added "shock" to the pool "every month or two". You need to know exactly how many PPM of CYA is in ea shock package.

    First, in pool chemistry, esp when the water is warming up, the difference btw one month and two months is huge. So, you need to document and be specific on the actual times you shock the pool over the exact time period.

    If you test what w your CYA is, then add shock, you will have to increase your CYA level by that much, minus any major water losses or water mixes [ie, 12-16" rain in 1-2 days].

    Keep good records by writing down dates and specific quantities. Also, as Rich suggested, the CYA test is very subjective. Just do it the same way [time, conditions & methodology] each time to be consistent.
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  5. Back To Top    #5

    Join Date
    May 2014

    Re: Not using pucks or a lot of shock but CYA keeps going up

    I'm reading this thread as someone who is still a learner; not a teacher, but doesn't TFP teach it's best to shock with bleach or other liquid chlorine? I know that dichlor and cal-hypo are not forbidden, but isn't it best to shock with bleach unless one is trying to concurrently raise CH or CYA and shock? Even if for no other reason, to keep PH from getting out of range?
    7600 gallon; 18'X54" round; vinyl; sand filter and 110V pump, 2-speed.
    Near Cookeville, TN--1/2-way between Nashville--Knoxville along I-40; Highland Rim part of the Appalachian Plateau (we call the Cumberland Plateau for the southern half of this geological region).

  6. Back To Top    #6

    Join Date
    Jan 2014
    Buckeye AZ

    Re: Not using pucks or a lot of shock but CYA keeps going up

    It's best to keep proper FC levels and then you NEVER shock. Pool stores get people in the habit of shocking once a month, or week, or whatever vague timeframe, to spike the chlorine temporarily. For a properly chlorinated pool (daily levels), you'll never need to shock.

    IF you have algae or other contaminants, or ammonia, then you would SLAM the pool, keeping the FC at shock level constantly. In this scenario, yes, it is advisable to just use liquid chlorine, so you are not constantly juggling effects of other additives like CYA, which will keep moving the target.

    And in general, it's very hard to remove CYA once it's in the pool, so better to start a bit low and ease your way to your target, once you are done clearing any algae issues.
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