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Thread: Understanding CYA and PH

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    Join Date
    Jul 2011
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    Understanding CYA and PH

    Hi guys. I am having trouble measuring my CYA. BY all accounts, I should have level 25 of CYA, but when I do the tube test, I can see the black dot (very faintly), no matter what. What am I doing wrong ? (by the way I put in this CYA directly into the skimmer a week ago)
    Also ---based upon how much CYA I put in. My PH should have gone down from 7.2 to 6.8--so as a result, I added enough borax to bring it back up .40 so it would remain at 7.2 ...instead my pool is at 7.8 or greater. Its almost like the stabilizer had no effect. What am I doing wrong ?
    Thanks in advance.
    21' All Steel AGP with Resin caps, Heyward S244T Sand Filter, Heyward 1HP 2 speed pump

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    JasonLion's Avatar
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    Re: Understanding CYA and PH

    There are really two separate issues here.

    First, you shouldn't ever adjust the PH in advance based on what the Effects of adding chemicals section of PoolMath says. Those are just rough approximations. Wait for the PH change to actually happen and then test and adjust from there.

    Second, it sounds like CYA did go up, just not as much as you expected. The CYA test is +-15, so you are well within the expected results. No adjustment is every going to come out exactly the way you expect it to. That is why you test, adjust, test again, and adjust from there as needed.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    bridgman's Avatar
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    Re: Understanding CYA and PH

    IIRC a barely visible dot when the tube is full *is* a reading of about 25 (it's just not accurate because "barely visible" could also mean 15 or 20).

    Did you put the CYA in a sock in the skimmer, or directly in the skimmer ? If the latter, and if you backwashed after adding the CYA, I think it would backwash any un-dissolved CYA out of your filter too.
    Cedar hot tub, 680 US gallons - Snorkel wood-burning heater, canoe paddle, "offline" Intex 1000 GPH pump/filter with skimmer

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    Re: Understanding CYA and PH

    Quote Originally Posted by bridgman View Post
    IIRC a barely visible dot when the tube is full *is* a reading of about 25 (it's just not accurate because "barely visible" could also mean 15 or 20).

    Did you put the CYA in a sock in the skimmer, or directly in the skimmer ? If the latter, and if you backwashed after adding the CYA, I think it would backwash any un-dissolved CYA out of your filter too.
    I put the CYA directly in the skimmer. But I didnt backwash for at least a week.
    21' All Steel AGP with Resin caps, Heyward S244T Sand Filter, Heyward 1HP 2 speed pump

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