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Thread: SLAM time again... How important is low CYA high PH before starting shock?

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    SLAM time again... How important is low CYA high PH before starting shock?

    Once again - I outsmarted myself thinking I would get away with opening the pool before the swamp took hold. A few warm days in February and March took care of that.

    Current chemistry:
    Chlorine: 0
    PH: 8+ adding 8 drops of acid demand bring it back into range - 9 drops instantly turn it yellow and put it below 7.0
    CYA: 30 or less
    TA: - 60
    Frogs: 5-6 that Ive seen

    I'm off to Tractor Supply for Muriatric acid.

    The muriatric is gonna lower the CYA even further. Is there a concern if I ignore the TA/CYA and get the SLAM underway?
    16x32 in-ground vinyl liner, SGS Breeze 540 salt system, Pentair 1.5hp pump, Booster pump & Tagelus sand filter.

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    Texas Splash's Avatar
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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    The muriatic acid should have no bearing on your CYA (stabilizer), only lowering the pH and TA. So definitely lower the pH right away since it's so high. Once you get it down to the lower 7s, you can increase your FC with regular bleach. Make sure you have at least 20ppm of CYA, 30 is ideal. Your SLAM/Shock level will be:
    FC of 10 for a CYA of 20
    FC of 12 for a CYA of 30
    Remember to follow everything listed on the SLAM page (link below) and don't stop until you pass all 3 SLAM criteria. AFTER you pass the SLAM, remember to increase your CYA to at last 70 to better support your SWG. Good luck.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
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    ned8377's Avatar
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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    Getting your PH to the low 7's will help your chlorine work better.
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    Quote Originally Posted by Texas Splash View Post
    The muriatic acid should have no bearing on your CYA (stabilizer), only lowering the pH and TA. So definitely lower the pH right away since it's so high. Once you get it down to the lower 7s, you can increase your FC with regular bleach. Make sure you have at least 20ppm of CYA, 30 is ideal. Your SLAM/Shock level will be:
    FC of 10 for a CYA of 20
    FC of 12 for a CYA of 30
    Remember to follow everything listed on the SLAM page (link below) and don't stop until you pass all 3 SLAM criteria. AFTER you pass the SLAM, remember to increase your CYA to at last 70 to better support your SWG. Good luck.
    Doh! I meant TA not CYA.

    Thanks for the quick response! This my 3rd SLAM - the only year I didn't have to do it was when I left the filter running all winter. Of course Mother Nature brought the coldest NC winter in years...LOL!

    - - - Updated - - -

    Quote Originally Posted by ned8377 View Post
    Getting your PH to the low 7's will help your chlorine work better.
    Hi Ned,

    I'm down in Fuquay.

    Thanks for the quick reply.
    16x32 in-ground vinyl liner, SGS Breeze 540 salt system, Pentair 1.5hp pump, Booster pump & Tagelus sand filter.

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    Texas Splash's Avatar
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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    If after lowering the pH you find the TA took a dive too much, just have some baking soda available to keep it over 50 at least. After your SLAM you can readdress pH and TA to see how best to keep them stable.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Mod Squad tim5055's Avatar
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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    Quote Originally Posted by ned8377 View Post
    Getting your PH to the low 7's will help your chlorine work better.
    While this is technically true for water with nothing else in it, once you add CYA to the water the effects of the pH are "buffered". Here is Chem Geek's explination:

    Quote Originally Posted by chem geek View Post
    With no CYA in the water, going from a pH of 7.5 to 8.0 lowers the active chlorine (hypochlorous acid) level by roughly 50%. With CYA in the water, not just at 30 ppm as in what I showed in the graphs bug higher levels as well, the same pH change only has the active chlorine level drop by 15%. So you can generally ignore the pH effect on chlorine. Cyanuric Acid is a buffer for hypochlorous acid so resists changes in the active chlorine concentration.
    So, with CYA in the water you can ignore the pH as far as effectiveness of the chlorine goes.

    We recommend pH in the low 7's to start a SLAM not because the chlorine is more effective, but because once the FC goes above 10 you will not be able to accurately test the pH. With all the brushing, pump running and other aeration during the SLAM we know the pH will rise, so start at the lower end of recomended.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    ned8377's Avatar
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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    Thanks Tim, I didn't know that CYA had that affect on PH but makes sense. There you go, learned something new again.

    Hello ggoodwinj3,

    TFP has been a life saver for me. I don't ever go to pool stores around here anymore. Got tired of being jerked around and being told 3 different things at 3 different stores.
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Re: SLAM time again... How important is low CYA high PH before starting shock?

    Quote Originally Posted by Texas Splash View Post
    If after lowering the pH you find the TA took a dive too much, just have some baking soda available to keep it over 50 at least. After your SLAM you can readdress pH and TA to see how best to keep them stable.
    Ever since I got the salt cell installed - I get the water balanced in the spring and almost never need to do much more than a fine tune once every week or 2.
    16x32 in-ground vinyl liner, SGS Breeze 540 salt system, Pentair 1.5hp pump, Booster pump & Tagelus sand filter.

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