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Thread: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

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    My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Hi! hope everyone is having a great summer. I would like to know if someone has some insight as to what can cause chlorine levels to drop so fast within hours. Here is the scenario. This past Saturday, at 10 am my FC was 5.5 ppm. My 2 kids (4 and 8), my wife and I started using the pool around 2pm and stop around 6 pm. Pool water was around 85 degrees and the air temperature around 85-90 degrees. When I tested the water this morning it was 2ppm. I am puzzle, as I did not think FC could be decrease so fast, especially when my salt chlorinator is working properly and ran as per schedule from 8pm to 5 AM. There was no storm/rain that night or anything I can think could cause such a significant decrease on my FC level. Any advice would be appreciated. Thanks.
    20,000 Gallons, 33.9 x 19.9 free form inground plaster pool 7 feet deep with Spillover Spa, Salt Generator (Fusion Soft),Heat Pump, Single Speed 2 HP Pump, D.E. Filter. Zodicac PDA, IQ900RS Controller.

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    Divin Dave's Avatar
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Hi,
    FC drops because of 2 reasons.
    1. UV from the sun
    2. Organics (including people) in the water like algae, grass, bugs, whatever...

    To be sure its not algae, do an overnight chlorine loss test. If there is 1 or less ppm drop in chlorine, then its not algae.
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge.
    www.tftestkits.net Experience- it's what's learned just after you needed it most !!

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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Thanks Divin!



    Quote Originally Posted by Divin Dave View Post
    Hi,
    FC drops because of 2 reasons.
    1. UV from the sun
    2. Organics (including people) in the water like algae, grass, bugs, whatever...

    To be sure its not algae, do an overnight chlorine loss test. If there is 1 or less ppm drop in chlorine, then its not algae.
    20,000 Gallons, 33.9 x 19.9 free form inground plaster pool 7 feet deep with Spillover Spa, Salt Generator (Fusion Soft),Heat Pump, Single Speed 2 HP Pump, D.E. Filter. Zodicac PDA, IQ900RS Controller.

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    Mod Squad pooldv's Avatar
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Don't forget potty breaks! If those aren't happening out of the pool then that is using up some chlorine. It is a good idea to up the chlorine level a couple of ppm before and after a big day of swimming. It is safe to swim with FC above minimum and up to shock level for your CYA. FC below minimum level is not properly sanitized.
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    ozdiver's Avatar
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    What is your CYA level?
    It is the Chlorine Sunscreen.
    40k gal freeform, IG pebblesheen, 9'x'6' raised spa, 2-1/2 hp Whisperflo, 520 sq/ft cartridge, Legend w/ booster, Intellibrite 5g in pool @ spa, Rainbow 320 Chlorinator(retired),
    Mastertemp 400k BTU, 3x3 hp Whisperflo Swimjets, 2x2 hp Whisperflow for 15ton moss rock waterfall, Intelitouch Controller, 850 sq/ft Travertine deck, Gas/Wood firepit,
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    My CYA level is 80. What do you mean by "sunscreen"?


    Quote Originally Posted by ozdiver View Post
    What is your CYA level?
    It is the Chlorine Sunscreen.
    - - - Updated - - -

    My kids take potty breaks outside the pool....I have a "urine detector" warning sign posted and my kids think the water will turn red if they do it in the water.



    Quote Originally Posted by pooldv View Post
    Don't forget potty breaks! If those aren't happening out of the pool then that is using up some chlorine. It is a good idea to up the chlorine level a couple of ppm before and after a big day of swimming. It is safe to swim with FC above minimum and up to shock level for your CYA. FC below minimum level is not properly sanitized.
    20,000 Gallons, 33.9 x 19.9 free form inground plaster pool 7 feet deep with Spillover Spa, Salt Generator (Fusion Soft),Heat Pump, Single Speed 2 HP Pump, D.E. Filter. Zodicac PDA, IQ900RS Controller.

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    ozdiver's Avatar
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    CYA is the thing that help protect Chlorine from Sun burnoff. (Hence Chlorine Sunscreen)
    Just making sure you had some in there. In fact you hav a LOT in there.
    If 80 is an accurate reading ( I hope it is not):
    Your Target FC for that level of CYA is 10 with a minumum of 6.
    That would indicate you are not maintaining sufficient FC to prevent Algae.
    40k gal freeform, IG pebblesheen, 9'x'6' raised spa, 2-1/2 hp Whisperflo, 520 sq/ft cartridge, Legend w/ booster, Intellibrite 5g in pool @ spa, Rainbow 320 Chlorinator(retired),
    Mastertemp 400k BTU, 3x3 hp Whisperflo Swimjets, 2x2 hp Whisperflow for 15ton moss rock waterfall, Intelitouch Controller, 850 sq/ft Travertine deck, Gas/Wood firepit,
    Autofill, TF-100 test kit w/ SpeedStir

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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Quote Originally Posted by ozdiver View Post
    CYA is the thing that help protect Chlorine from Sun burnoff. (Hence Chlorine Sunscreen)
    Just making sure you had some in there. In fact you hav a LOT in there.
    If 80 is an accurate reading ( I hope it is not):
    Your Target FC for that level of CYA is 10 with a minumum of 6.
    That would indicate you are not maintaining sufficient FC to prevent Algae.
    Res, with a SWG it's perfectly fine and recommended to keep your CYA between 60-80 so yours is right in range. I keep mine at 80 as well and target my FC around 8 since my pool has absolutely no shade from 8;00 AM - 6:00 PM in the blazing Charleston sun. After you post your OCLT results, we'll see what next steps might be.
    5900 G Fiberglass IG pool (circa 1990), SWG Hayward Aqua Rite GoldLine (2013), IntelliFlo Variable Speed Pump (2013), Hayward Pro Sand Filter (circa 1990), Well water (no iron or other metals fortunately), test with Taylor K2006C, Charleston, SC

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    ozdiver's Avatar
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    My apologies, I missed the SWCG.
    I'm obviously a bleacher so my targets are lower.
    40k gal freeform, IG pebblesheen, 9'x'6' raised spa, 2-1/2 hp Whisperflo, 520 sq/ft cartridge, Legend w/ booster, Intellibrite 5g in pool @ spa, Rainbow 320 Chlorinator(retired),
    Mastertemp 400k BTU, 3x3 hp Whisperflo Swimjets, 2x2 hp Whisperflow for 15ton moss rock waterfall, Intelitouch Controller, 850 sq/ft Travertine deck, Gas/Wood firepit,
    Autofill, TF-100 test kit w/ SpeedStir

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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Thanks for the replies and advice. I slamed my pool and then tested. The chlorine levels did not drop more than 1ppm. FC level are ok since. So all, I can think is that some animal went for a swim in my pool that night. I lived in an area wood lots of woods behind my yard. T
    20,000 Gallons, 33.9 x 19.9 free form inground plaster pool 7 feet deep with Spillover Spa, Salt Generator (Fusion Soft),Heat Pump, Single Speed 2 HP Pump, D.E. Filter. Zodicac PDA, IQ900RS Controller.

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    ozdiver's Avatar
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    Re: My chlorine level drop from 5.5 ppm to 2ppm within 12 hours?????

    Great to hear you got it straightened out.
    40k gal freeform, IG pebblesheen, 9'x'6' raised spa, 2-1/2 hp Whisperflo, 520 sq/ft cartridge, Legend w/ booster, Intellibrite 5g in pool @ spa, Rainbow 320 Chlorinator(retired),
    Mastertemp 400k BTU, 3x3 hp Whisperflo Swimjets, 2x2 hp Whisperflow for 15ton moss rock waterfall, Intelitouch Controller, 850 sq/ft Travertine deck, Gas/Wood firepit,
    Autofill, TF-100 test kit w/ SpeedStir

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