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Thread: What causes CYA to increase?

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    What causes CYA to increase?

    I can't seem to find the answer anywhere. My CYA is at 100ppm, had been at 50-60ppm last summer. What caused the increase? I use an inline chlorinator with 3in tabs and calcium hypochlorite shock. 10k pool.
    Houston
    ~20,000 inground plaster pool
    1.5 HP Hayward
    Sand Filter

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    Butterfly's Avatar
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    Re: What causes CYA to increase?

    Your tabs contain CYA. They are the number one reason for pools becoming overstabilized, as yours is. You need to do a series of drains/refills to exchage about half your water to reduce your CYA to around 50 or so. In fact, the test may read your CYA as 100, but it may actually be higher than 100. You will be able to test closer after you do the drain/refill dlance.

    Also, you need to switch from the tabs to liquid chlorine or plain 6% bleach, which unlike the tabs, have no unwanted side effects.

    You should post a full set of test numbers so we can have a better response. Since you have been shocking with cal hypo, your cal may be too high, too.

    Stop shocking until you get the CYA down and post a full set of test results. It is very difficult (and expensive!) to shock a pool with 100 or more CYA !

    Please go to Pool School - white button at top right of each page - and do some reading to help you understand the process. Pool School is a great teacher

    Post back with any questions you may have. Someone is always here to help.

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    Ohm_Boy's Avatar
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    Re: What causes CYA to increase?

    Most likely, it's those 3in trichlor tabs, which add 0.6ppm CYA for every 1ppm of chlorine. The chlorine gets used up, but the CYA just accumulates. As an aside, your calcium level might be a bit high too, from the cal-hypo - it's worth getting a full test with a good kit.
    Basically, for the CYA level to just go up requires either a source of CYA being added to the water, or errors in the test results. Or both. Evaporation isn't usually a factor, as it will allow the concentration to go up as the water goes away, but when make-up water is added the concentration goes back down.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

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    Re: What causes CYA to increase?

    I test weekly with test strips and then take my water to Leslie's monthly for a more complete test. I tested at Leslie's last week and will post those results when I get home.

    The only things that were out of range were CYA at 100 and Phosphates were high (can't remember the number). Everything else was "in range".

    The water is crystal clear.
    Houston
    ~20,000 inground plaster pool
    1.5 HP Hayward
    Sand Filter

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    JasonLion's Avatar
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    Re: What causes CYA to increase?

    The pool stores concept of "in range" and ours are likely to be very different. For example phosphates don't matter, pool store testing for phosphates is mostly about making sales of expensive phosphate remover to people who don't really need it. You will have far more control over your pool, and save money, if you knew what your levels really were.

    You really need to get your CYA level down. With CYA around 100 it is very difficult to prevent algae. You should also think about stopping using trichlor tablets, which are constantly adding more CYA.
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    Re: What causes CYA to increase?

    Dichlor (a form of granular chlorine) also contains cyanuric acid. Be careful not to use any of that.

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    Re: What causes CYA to increase?

    Just to put some perspective on this, if you had not been using any Cal-Hypo and only used Trichlor pucks/tabs, then even at a low 1.5 ppm FC per day chlorine usage, the CYA level would increase by almost 30 ppm PER MONTH. Also note that Cal-Hypo is not without side effects as it raises Calcium Hardness (CH). The following are chemical facts that are independent of pool size or concentration of product:

    For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
    For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
    For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

    Chlorinating liquid or bleach will not increase CYA nor CH.
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    Isaac-1's Avatar
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    Re: What causes CYA to increase?

    Just follow up a little here, trichlor tabs/pucks, etc. worked great when they came out several decades ago when water was cheap, and pools were made out of concrete, and similar material and were routinely drained in the off season. You would start with a fresh fill in the spring time, and the CYA level would be just getting to the unmanageable level in the fall when it was time to drain the pool for the winter. Most people today no longer have the luxury of draining their pools in the off season either due to pool construction materials or the associated cost of water, so in trichlor and dichlor maintained pools we see the ever increasing CYA levels and all the problems they cause, worse yet the pool industry as a whole does not recognize the details of how CYA effects chlorine performance, the typical pool store approach is to keep trying to fight the symptoms by adding more and more expensive chemicals like algaecides to the water, before eventually giving in and telling the customer something like the water has became old or stale and should be replaced.

    Ike

    p.s. on one other note, test strips have issues in all their values, but are nearly useless at measuring CYA level
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