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Thread: Do I know what I think I know?

  1. Back To Top    #1

    Do I know what I think I know?

    20K Gallon IG vinyl
    Boston Ma, full sun all day
    PH 7.4
    CYA 45
    TA 80
    TC 8.5 / CC .5 (first thing this AM after last night's bleach dose)
    Pool currently excellent clarity

    In past years, combining Tri-Chlor pucks with reliance on simple OTO tests advising 1.0 to 3.0 Min-Max levels has not worked well. I was (I think) always under-chlorinated with algae spots, and the Min-Max scale (I've learned) does not account for CYA levels. This year, I'm going with nightly bleach. Here's my plan... please confirm I'm on the right track, or offer corrections where appropriate.

    1. Keep Chlorine no less than 3 (maybe even 4 with 45 CYA and full sun??).
    2. Add Chlorine each evening so it can sanitize overnight before the sun hits it next day.
    3. Establish typical daily chlorine consumption by testing (FAS/DPD) a few cycles over several mornings and evenings:
    - each evening (before chlorine addition) to get a daily baseline
    - early each morning to determine overnight sanitizing consumption
    A few of these cycles should tell me what is lost overnight sanitizing, what is lost each day to sun and sanitizing, and combining the two I'd get typical total daily consumption.
    4. Using Calculator, determine typical nightly Chlorine dose needed based on typical daily consumption to stay near but above minimum level while adding enough for daily consumption.

    Is this basically what those of you who use bleach do? Do you test every night, or establish typical daily bleach dosage and then only test every 3 days or so? Do you adjust chlorine dosage up or down based on swimmer load and/or sun/overcast? If so, how much affect would, for example, 5 adult swimmers for 2 hours affect consumption? At CYA of 45, how much is consumption affected by a day of full sun versus overcast-or-rain? And how does significant rain (say > 1/4 inch) affect Chlorine consumption?

    I'm not as anal as I sound, but I'm trying to establish some baselines so if I'm out of town, I can give reasonably simple instructions to neighbors on how much bleach to put in each night with dosage adjustments for heavy use, sun, overcast or rain.

    Thanks for youre indulgance of this post.
    Greater Boston area
    20,000 Gal IG Vinyl
    48 sq ft DE panel filter
    1 HP Hayward Pump
    Full Sun exposure all day

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Do I know what I think I know?

    You only need to test once a day, preferably in the evening, and add enough chlorine so you are still at or above your minimum the next evening. After several days of that, you will know the right amount of chlorine to add and can just add it with only a quick check with OTO to make sure nothing is going wrong. Then weekly you do the full FAS-DPD chlorine test again to see if you need to update your amount of chlorine based on changes in the seasons etc.

    Overnight chlorine loss will be zero if everything is working correctly. WIth a little practice you will be able to tell if everything is working correctly or not simply by looking to see how the water looks, does it sitll have it's sparkle or not.
    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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