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Thread: CYA increased...but how?

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    CYA increased...but how?

    We starting using the chlorine tablets basically just the first day we opened the pool and then I came on here and learned that's a terrible thing to do , so we shut off the chlorinator and have been using strictly liquid chlorine since then, meaning we have only been using liquid chlorine the past 3 weeks, no tablets.

    Our CYA was at 40 at that time and had been pretty steady there. (At least I assume it has been steady. I only tested it a few times thereafter and then haven't tested it in a few weeks because there was no reason to (i.e., no water replacement, etc, except for lots of rain). We were going by the chlorine/CYA chart using our CYA of 40 to determine our FC target levels.

    Just tested today on a whim (no real reason to) and CYA seems to be at 50.

    FC: 5
    pH: 7.5
    TA: 100
    CYA: 50

    What would cause this increase? Is this just the residual effect of that one day (don't even think it was a total day) of using the tablets, taking weeks to affect our CYA level?
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: CYA increased...but how?

    It can take a couple of weeks for CYA from solid sources to show on your test.
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    Re: CYA increased...but how?

    Test test result can vary +/- 10 ppm, depending on when you test, ambient light, and other factors.

    The only way for CYA to get into a pool is by someone adding it.

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    Re: CYA increased...but how?

    Quote Originally Posted by 257WbyMag
    Test test result can vary +/- 10 ppm, depending on when you test, ambient light, and other factors.
    .
    When is the best time to test? Evening?
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: CYA increased...but how?

    Quote Originally Posted by RobbieH
    It can take a couple of weeks for CYA from solid sources to show on your test.
    Is it likely that that small amount of tablets could have increased the CYA that much (if this increase is not due to a tester error)?
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: CYA increased...but how?

    One or two tablets don't add that much.

    I try to test at the same time of day and with the same conditions while standing in the same spot. Because the test is so dependent on the amount of light entering the tube from the sides, it is important that the light during testing is consistent in its intensity.

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    Re: CYA increased...but how?

    Quote Originally Posted by 257WbyMag
    One or two tablets don't add that much.

    I try to test at the same time of day and with the same conditions while standing in the same spot. Because the test is so dependent on the amount of light entering the tube from the sides, it is important that the light during testing is consistent in its intensity.
    Ok, makes total sense, and a bit of a relief because I actually think I tested this time in more of a shady spot because it's so hot I was trying to avoid the sun This test is probably off what the true CYA is due to that. I'll have to retest.

    Thank you!
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: CYA increased...but how?

    CYA should be tested when there is bright sunlight and the sun is to your back, and the tube should be viewed from arms length. Testing in shaded areas will tend to result in higher readings. Try it yourself measure as described above, then step into the shade and watch the dot show up as if by magic.
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    Re: CYA increased...but how?

    Thanks guys. I just retested and I realize how significant the conditions can change your reading!

    I have a totally unrelated question, but I wasn't sure where to post it.

    I was just thinking about how we shut off the chlorinator a few weeks ago. I had my husband shut it off, but I just remembered that I think there may be some tablets in there still. Since it has been totally shut off, and it's been hot outside, if he opens it up, will it explode or something? I really want those tablets out of there before it gets even hotter, but it doesn't seem safe at all to open that thing since it's not ventilated. Not sure what to expect. There's no reason I want to get the tablets out other than my thinking that they aren't safe in there, so if they can do no harm in there when the chlorinator is shut off, I would just leave it be.
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: CYA increased...but how?

    Anyone, anyone? Maybe this is the wrong spot to post my question above regarding the chlorinator? If so just let me know where

    Really curious about how to go about our issue. Even wondering if we should turn it on and let them run through (probably about 5 tablets in there) the pool just to get them out rather than opening the chlorinator and manually removing them. Let me know what y'all think!
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: CYA increased...but how?

    Just to clarify...

    using tablets isn't necessarily terrible. Using tablets ONLY is not good because it raises your CYA and lowers PH....but if you are aware of this, then you can use tablets when you need to raise your CYA and lower your pH when you actually need it.

    In regard to opening the chlorinator, there is no danger, as far as I know.

    If and when you get a heavy rain and you need to drain some of the pool, realize you will also be lowering CYA. Depending on how often this happens, you may want to turn on the chlorinator occasinally to raise the CYA again, but realize, this will also lower your pH.
    8,000 gallon, in ground, fiberglass pool with a cartridge filter.

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