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Thread: Surprised TA is down and CYA is steady. Why?

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    Surprised TA is down and CYA is steady. Why?

    New IG pool built August 2013, opened mid September 2013 and starting using my TF-100 test kit. At that time my TA was 240 so I added muriatic acid in early Oct according to pool calculator which brought it down to 190 on Oct 7, 180 on Oct 12, and 160 on Oct 18 and then pool was closed for season. I only added muriatic acid once in the beginning of Oct. Also, I've been using 3" trichlor pucks in a Hayward CL-200 chlorinator since the pool opened - initial CYA was 0 but I brought it up to 30 using pool calculator recommendation before pool was closed for the season.

    Pool opened early May 2014 (love the heater) and my readings on May 4 and today (June 15):

    Cl 5 (1)
    CC 0 (0)
    pH 7.8 (7.5)
    TA 150 (110)
    CYA 30 (30)
    CH 300 (280)

    Note: I check the Cl and pH weekly and until today's low chlorine reading they have both been steadily Cl of ~5 and pH of ~7.5. I adjusted the setting on the chlorinator today to increase the Cl, not sure if that dial really works so we'll see.

    1) Why is my TA going down? The pool has been used by my 3 kids about once per week this season so far which seems light, except for one birthday party for my son where 15 kids were splashing in the pool for 2 hours - could that aeration have done it? TA is in range at 110 so I don't plan to do anything right now, I'm just surprised it's dropping like that.

    2) Why is my CYA holding steady at 30 since I'm using the trichlor pucks, which from reading this site I understand should be raising CYA? The pucks I use are 99% trichloro-s-tirazinetrione, 1% inert ingredients, 90% available chlorine. I was expecting to see it start to clime and have to start using bleach instead.


    IG 18x36 polymer walls, vinyl liner, 24K gallons, Hayward SwimClear Cartridge Filter, Hayward 1 HP Super Pump, Hayward Universal H-Series Low NOx Heater 250K BTU Nat Gas, Hayward CL200 Chlorinator, Hayward ColorLogic 4.0 Lighting, Merlin Smartmesh Safety Cover, Binghamton NY area

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Surprised TA is down and CYA is steady. Why?

    Trichlor tablets are acidic, which lowers both PH and TA. PH can go up from aeration, but TA remains lowered.

    CYA only goes up slowly from using trichlor tablets. The CYA test is also not all that precise. So the CYA level can go up a fair bit and still not show up on the test. CYA can also be lowered by any water replacement you might have (overflow, backwashing, etc).
    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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