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Thread: Numbers after CYA adjustment

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    joshearl's Avatar
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    Numbers after CYA adjustment

    The pool is up to a warm 75f today and it looks like my numbers are finally after waiting a week for the CYA to settle in:

    FC: 2
    pH: 7.6
    TA: 90
    CH: 140
    CYA: 54

    The pool gets direct sunlight all day and from sundown at 7:30pm last evening until just now at 2:20pm the next day FC has only dropped .5ppm with no CC. This seems like a good rate to be dropping at, right?

    I'm a bit worried about the CH level being so low. I'm assuming the need to purchase some calcium chloride dihydrate and raise up 120 ppm. Looking at some of my old numbers, my CH has been at 140 and no one has advised to raise it. Does this mean it is fine?

    Anyway the water is warm and I'm looking forward to taking my first dip in after some yardwork today!
    25,000gal Plaster
    Pentair Nautilus NS-60 DE Filter

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    Mod Squad zea3's Avatar
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    Re: Numbers after CYA adjustment

    You should keep CH between 250-350 for a plaster pool as per the recommended levels chart.
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    Re: Numbers after CYA adjustment

    FC drops as a percentage not just as a ppm value. So if you use the FC target of 7 (minimum 5) from the CYA chart, you may indeed see the expected drop of something like 2 ppm per day since that'd be about 25% of the FC. Not that 25% is the drop you expect, but that 25% is the percentage drop you saw from 2.0 to 1.5, assuming those numbers are exact which they probably are not.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    joshearl's Avatar
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    Re: Numbers after CYA adjustment

    Ok that makes sense anonapersona! So what kind of drop should I expect/shoot for on a normal day to day basis now? I get full sun all day btw. I got my FC and CH up to par btw, current pool numbers:

    FC: 7
    pH: 7.6
    TA: 90
    CH: 265
    CYA: 54

    When I added the calcium I ran the pump for a couple hours and as the sun was setting the water was shimmering beautifully, clearer then I have ever seen it. Is this what happens when you normally add calcium? I've have used Ultra Bright blue stuff in the past and it never made it this clear!
    25,000gal Plaster
    Pentair Nautilus NS-60 DE Filter

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    Re: Numbers after CYA adjustment

    josh,

    1. That's not enough chlorine loss to be accurate. How are you testing? You should have dropped AT LEAST 2ppm based on your description.

    2. If your CYA test result is close, you should be keeping FC higher....around 4-6ppm.

    3. Your water is sparkling because you have done a good job with your chemistry, but you're gonna' need more chlorine to keep it that way.

    4. Yes, your CH is too low but I would focus on better test results and raising the FC first, and then address the CH.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    joshearl's Avatar
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    Re: Numbers after CYA adjustment

    Thanks duraleigh.

    I tested the FC loss with a TFP kit, using the 'within .5ppm' instructions. I will test the overnight loss again at .2ppm to make sure things are good. I realized my FC was too low (junk DPD kit is not accurate at all!) and I upped it while I upped my CH.
    25,000gal Plaster
    Pentair Nautilus NS-60 DE Filter

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    Re: Numbers after CYA adjustment

    Yeah, redo that FAS/DPD chlorine test from sundown to sunup and see what you get. It's called the OCLT and you can find instructions on how to do it up in pool school.

    A PERFECT pool will usually lose .5ppm (or less) during the dark hours and then another 2-4ppm during daylight depending on bather load, sun exposure, temp, etc.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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