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Thread: FC holding overnight, going to zero during day

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    FC holding overnight, going to zero during day

    I've recently been through the shocking process and passing the OCLT for the past couple days. The pool looks great, finally.

    However, I should be past the shocking process now, and am targeting FC of 4 since my CYA is at 30. I can get this and hold it overnight just fine.

    However, when I come home from work two days in a row now, FC is at 0. I live in the central valley of CA which is very hot and has a lot of direct sunlight. The pool is in direct sun basically all day. It's been over 100 deg F the last couple days.

    Is the prescription to raise my CYA to help hold FC up during the day?
    10k gal IG w/ salt system, spa, gas heater, and auto cover.

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    Re: FC holding overnight, going to zero during day

    My pool get full sun most of the day and I have raised my CYA level to 55 to help combat the loss of chlorine.
    18x36 Vinyl In-ground w/roman ends 27,400G, Hayward 3/4hp with 300# sand filter. Hayward heat pump heater

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    frogabog's Avatar
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    Re: FC holding overnight, going to zero during day

    You should be targeting the maximum FC for your CYA level of 30, which I think is closer to 7ppm. (check pool calculator). The reason you're losing all the chlorine, is that you don't have enough in there to lose it and still have the minimum (3ppm).

    So... do this instead:

    Dose to the maximum at night (7ppm). Check in the AM that it's still 7ppm. At the end of the day, check again. It should be above 3ppm. Dose again back to 7ppm. Rinse and repeat... forever :~}

    That should solve your loss issues.

    edit: you won't have to test every evening and morning after a while. Only at night, and only if you think you need to. The first time though, test to be sure it's all as it should be for a maximum nightly dosing regimen.
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

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    Richard320's Avatar
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    Re: FC holding overnight, going to zero during day

    What he said ^

    I'd raise CYA, too. You can add it as stabilizer, dichlor "shock" or trichlor pucks. Just be careful how much of the powders or pucks you buy, so you don't overdose the CYA. One 8 oz. puck will jack CYA almost 2 ppm in your pool. So the huge economy size pail is too many pucks.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    chessie6's Avatar
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    Re: FC holding overnight, going to zero during day

    I had the exact same problem last year when my cya was at 30. My pool gets direct sunlight from 10 am to 7 pm. This year I've raised my cya to 40-45 and what a difference in how well the chlorine holds.
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    Summer: 19 x 37 Pacific Graphex IG modified oval, aztec marine vinyl liner, 24,000 gal, 3.5 feet to 8 feet, 1 hp Hayward C4025 Swim Clear 4-cartridge filter, 12.5% Liquid Pool Shock for sanitizing, 1 super wide mouth skimmer, 4 returns (2 therapy jets in steps), Hayward Heat Pro heat pump, non-curved pool slide, 6' jump board, 8 ml blue solar cover, TF-100 test kit, had pink algae in 2010 Winter: Hot Springs Vista Spa, 500 gallons.

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    techguy's Avatar
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    Re: FC holding overnight, going to zero during day

    I am in Sacramento and my FC loss has been close to 4FC on a regular basis. My CYA is close to yours. I don't use a cover.
    -- Guy --
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    frogabog's Avatar
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    Re: FC holding overnight, going to zero during day

    Quote Originally Posted by Richard320
    What he said ^
    Richard, Richard, Richard...

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    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  8. Back To Top    #8

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    Re: FC holding overnight, going to zero during day

    Alright, I'll try going up to 7 and see if that leaves me anything at the end of the day.

    I'll also use some dichlor that I have laying around from my "pool store advice" days and see if I can get my CYA up to 40-50 range.

    Thanks again!

    I'm already eyeing that "automation" forum...lol.
    10k gal IG w/ salt system, spa, gas heater, and auto cover.

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    frogabog's Avatar
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    Re: FC holding overnight, going to zero during day

    Remember to raise your high nightly target once you get the CYA raised. I think you'll be pleasantly surprised to find chlorine in your pool tomorrow evening after doing this. It's worked well for me going on three seasons now. If you're losing more than 4ppm per day after raising your nightly to 7ppm, do 7.5 and see where it falls to the next evening. The general rule is ~50% loss per day, so I think you'll see a loss closer to 3.5 after you change this leaving you well above minimum.

    Raising CYA to 40 will likely help. Try 40 for a week or so before you bump up to 50 just to be sure you need more.
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  10. Back To Top    #10

    Re: FC holding overnight, going to zero during day

    Ditto on the 50% loss..here in kc in order for me to have a 5fc at the end of the day, I have to bring it up to 11 at night so that the end of the next day it is around 5 again....I think im running around 40cya...These HOT summer days really zaps the fc during the day

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    Re: FC holding overnight, going to zero during day

    I aslo run my fc at the higher end of the scale to give me a little cushion on changing conditions

  12. Back To Top    #12

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    Re: FC holding overnight, going to zero during day

    Quote Originally Posted by frogabog
    If you're losing more than 4ppm per day after raising your nightly to 7ppm, do 7.5 and see where it falls to the next evening. The general rule is ~50% loss per day, so I think you'll see a loss closer to 3.5 after you change this leaving you well above minimum.
    Pretty darn close.

    I raised it to 7 last night, it was about 3 when I got home today.

    Problem solved. Getting the hang of this...
    10k gal IG w/ salt system, spa, gas heater, and auto cover.

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