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Thread: Pool Test: CYA High / TA and PH Low

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    Join Date
    Jul 2014
    Location
    Atlanta, Georgia
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    Pool Test: CYA High / TA and PH Low

    First time owner of a pool and we have been struggling with our pool this summer.

    I just returned from Leslie's and the results of our pool test:
    FC - 2
    PH - 7.2
    TA - 40
    CH - 160
    CYA - 90

    I have spent hours on this site reading the different posts and I have learned so much but I still have questions. Our pool water is crystal clear right now. Using the pool calculator here is my course of action

    1) Add one gallon and 3/4 quart (149 ounces) of chlorine bleach purchased at Wal-Mart. My goal is the increase FC to 4.
    2) Add 21 lbs (337 ounces) of baking soda. My goal is to increase TA to 80.


    I have some questions:
    1) What is the difference in the pool calculator between ounces by weight or volume?
    2) I believe I read on this website that adding the bleach will also increase the PH. Do I wait until the FC has increased to 4.0 and then retest the PH before I fix the PH level?
    3) The Chlorine / SWG Chart on this website has a maximum CYA level of 80. Is 90 that much higher that I need to take corrective action? Because my CYA is 90 do I need to increase my PH level to 6?
    4) The pool store wants my CH to be between 200 and 400. I believe I read on this site that because I have a vinyl pool I do not need to be adding any CH. Is this correct?

    I know I have a lot of questions so I just want to say thanks in advance for your time in answering them. Thanks!
    35,000 Gallon Inground Pool 20' x 40' / Vinyl Liner / Pentair IC40 SWG / Hayward Sand Filter
    First time pool owner in 2014 but pool is about 6 years old

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: Pool Test: CYA High / TA and PH Low

    Welcome to TFP!

    1) Weight you measure with a scale. Volume you measure with a measuring cup.
    2) Bleach has no net effect on the PH. (Ignore the transient effects.)
    3) 90 isn't the end of the world, hopefully it will drift down through the season. FC target is 4 to 6, never below 4.
    4) There is never any reason to add CH to a vinyl liner pool (except the occasional warranty requirement).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Join Date
    Jul 2014
    Location
    Atlanta, Georgia
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    Re: Pool Test: CYA High / TA and PH Low

    I wonder if the pool store tested the level of CYA accurately. The CYA level has been steady around 40 for the last 3 tests over a 6-8 week period. Before I found this website, I followed pool store instructions, and added 5 bags of Shock, to increase the chlorine level. Based on reading here I understand that this is the cause of my increase in CYA. Is it reasonable for the 5 bags to raise the CYA from 40 to 90? I run my pump 10 hours a day and I added the shock three days ago and tested today. Is it likely the 5 bags more than doubled the CYA or is the pool store test off?
    35,000 Gallon Inground Pool 20' x 40' / Vinyl Liner / Pentair IC40 SWG / Hayward Sand Filter
    First time pool owner in 2014 but pool is about 6 years old

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    JasonLion's Avatar
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    Re: Pool Test: CYA High / TA and PH Low

    Pool store test results are notoriously unreliable. If it has measured at 40 for several visits, there is no way it can be 90 now unless you have added stabilizer or used a bunch of dichlor or trichlor. You say added "shock". That could be any of several different chemicals, one of which is dichlor. Dichlor contains huge amounts of CYA. But it could also be cal-hypo, which doesn't contain any CYA. If you don't know the chemical name, we can usually figure it out from the brand name.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Join Date
    Jul 2014
    Location
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    Re: Pool Test: CYA High / TA and PH Low

    I've been adding the Shock with Dichlor so I am going to assume the level of CYA is greater than 40 but nowhere near 90. I am going to wait for my TF-100 test kit to measure myself before I say I know for sure the level of the CYA. Until I can test it with my kit what should I aim for the FC? Still 4 to 6?

    Thanks.
    35,000 Gallon Inground Pool 20' x 40' / Vinyl Liner / Pentair IC40 SWG / Hayward Sand Filter
    First time pool owner in 2014 but pool is about 6 years old

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    JasonLion's Avatar
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    May 2007
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    Re: Pool Test: CYA High / TA and PH Low

    It would take 28 lbs of dichlor to raise CYA by 50 in 35,000 gallons.

    Guess at a likely number for your CYA level assuming the reading of 40 was correct and how much dichlor you used and then use the FC target level for that.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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