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Thread: What does it mean when you say the sun "burns off" chlorine?

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    What does it mean when you say the sun "burns off" chlorine?

    Does that mean that it breaks it down so that it re-bonds in the pool? I can't imagine it just turns into chlorine gas and escapes...does it? Otherwise, the principal of an SWG wouldn't seem to work (you'd have an ever-falling level of chlorine with nothing for the sodium to bond to).

    So can someone explain that to me? I don't need to know for any maintenance purposes...I'm just a dyed-in-the-wool geek.
    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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    gboulton's Avatar
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    Re: What does it mean when you say the sun "burns off" chlor

    From waaaaaaaaaaaaay back in the dusty corner of my brain, during a conversation about de-chlorinating tap water for fish tanks, I seem to remember...

    2OCl- --> O2 + 2Cl-

    Our bleach produces Hypochlorite ions, which do the work of destroying organics. However, they're relatively unstable, and bombardment by UV light splits them into O2 (Oxygen molecules) and a Chlorine ion...which then, yes, outgasses.

    I'm betting chem geek can come along and provide a more thorough and descriptive answer, but that's what my dusty old memory tells me anyway.
    -Gordon
    Pool School helps me maintain my 13,500G 24' x 48" ASP with Sand Filtration using a TF100 Test Kit and Pool Calculator.
    Remember, the Shock Process should be followed until : 1. CC is less than 0.5 ppm, 2. An OCLT shows a loss of 1.0 ppm or less and, 3. The water is crystal clear.
    --I didn't buy my pool to swim in it. I bought my pool to watch my wife swim in it. :wink:

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    JasonLion's Avatar
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    Re: What does it mean when you say the sun "burns off" chlor

    The detailed chemistry is explained in this post. The oxygen gas escapes, but the chloride ion stays in the water, essentially it becomes salt.
    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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    Re: What does it mean when you say the sun "burns off" chlor

    Thanks! So MUCH info here! The "dad" and "pool owner" in me are fighting with the "engineer" and "geek" in me for which to consume first!!

    I'm an IT guy by trade, an electrical engineer by degree and a geek in every other way. I set the class curve in chem in college (means nothing now, of course), but I *loved* chemistry back then! It was like math with consequences!
    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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    gboulton's Avatar
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    Re: What does it mean when you say the sun "burns off" chlor

    Thanks for that link, Jason. Good stuff! I see my memory was "ok" but significantly oversimplified, and wrong about outgassing. Thanks for offering education.
    -Gordon
    Pool School helps me maintain my 13,500G 24' x 48" ASP with Sand Filtration using a TF100 Test Kit and Pool Calculator.
    Remember, the Shock Process should be followed until : 1. CC is less than 0.5 ppm, 2. An OCLT shows a loss of 1.0 ppm or less and, 3. The water is crystal clear.
    --I didn't buy my pool to swim in it. I bought my pool to watch my wife swim in it. :wink:

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    Re: What does it mean when you say the sun "burns off" chlor

    Even the post I wrote that Jason linked to is an oversimplification, but shows the net result. In reality, the UV in sunlight breaks apart chlorine into radicals which eventually produce chloride ion and oxygen gas (technical details in this new post).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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