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Thread: Chlorine smell questions

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    peterdaly's Avatar
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    Chlorine smell questions

    I've gotten indications from discussion here that, generally, FC has no odor, but CC has that "public pool smell" of chlorine. So, by extension, if my pool has the chlorine smell at times, that would be indication of organics (etc) being actively attacked by my (previously) FC...which is no longer free.

    Is that right, or am I jumping to conclusions?

    If that is correct, do public pools reek because they are essentially dirty pools, resulting from high bather load?
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    Smykowski's Avatar
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    Re: Chlorine smell questions

    You are correct.
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    Re: Chlorine smell questions

    I posted a similar thread recently.

    http://www.troublefreepool.com/threa...ell-in-morning

    maybe some useful info for you

    crazy humid this morning - could cut the air w/ a knife - and, I could smell a faint Chlorine smell when I was right next to the pool
    It isn't an off putting smell - but, I can smell a bleach smell.

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    Re: Chlorine smell questions

    It really is not that they are dirty. Public outdoor pool usually don't smell. Public indoor pools and changing rooms smell because of decreased ventilation. Pool water with FC drips on the floor or deck with organics and combines just as it would in the pool. Yes it's the cc's you really smell. Even a bottle of open bleach. What you smell at the open top is the reaction with the atmosphere.
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    peterdaly's Avatar
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    Re: Chlorine smell questions

    Thanks guys. Seems to confirm my thoughts.
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    Re: Chlorine smell questions

    Quote Originally Posted by jcowart View Post
    It really is not that they are dirty. Public outdoor pool usually don't smell. Public indoor pools and changing rooms smell because of decreased ventilation. Pool water with FC drips on the floor or deck with organics and combines just as it would in the pool. Yes it's the cc's you really smell. Even a bottle of open bleach. What you smell at the open top is the reaction with the atmosphere.
    That's not true. Hypochlorous acid itself does smell and is what you smell (along with hypochlorite ion) rather strongly from concentrated bleach or chlorinating liquid (hypochlorite ion has a similar odor but is more limited in how much can be volatized due to charge imbalance though with bleach its concentration is much higher). You can have perfectly clean air and readily smell bleach and chlorinating liquid. It is a different kind of smell than the chloramines.

    The following table shows odor and taste thresholds from the paper "Aroma and Flavor Characteristics of Free Chlorine and Chloramines" (starting at page 75 as shown in this link) in the Proceedings of the American Water Works Association (AWWA) Water Quality Technology Conference (WQTC) in 1984.

    Compound ........... Descriptor ....... pH .. Odor . Taste
    Hypochlorous acid .. Bleach .............. 5.0 .. 0.28 .. 0.24
    Hypochlorite ion ..... Bleach ............ 10.0 .. 0.36 .. 0.30
    Monochloramine ..... Swimming pool . 8-9 .. 0.65 .. 0.48
    Dichloramine ......... Swimming pool .. 4.0 .. 0.15 .. 0.13
    Trichloramine ......... Geranium .................. 0.02

    People associate the monochloramine and dichloramine odor with swimming pools and not with bleach. It's the "bad pool" smell.

    At pool pH with a mixture of hypochlorous acid and hypochlorite ion, the thresholds would be roughly the average so roughly 0.32 ppm FC with no CYA. This is generally higher than the unbound chlorine level in pools with CYA except at shock level, but with churning of the water one can increase volatization and with pool covers one can build up higher concentrations in the air that are more noticeable until blown away. Also, the amount of volatization is a function of temperature so warmer pools or hot spas would smell more than cooler ones at the same chlorine level in the water.
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    Re: Chlorine smell questions

    An observation, for what it's worth. This spring when I slammed my pool, just before the slam was complete, when I walked out the back door of the house, I could smell the chlorine. When the slam was complete, no more smell.
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    peterdaly's Avatar
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    Re: Chlorine smell questions

    So with a well balanced pool, per the SWG guidelines on this site, is it far fetched to jump to the conclusion that "chlorine smell" could be attributed to organics, sunscreen, sweat, or urine in the pool?

    In other words, if you smell it, that means the chlorine is doing it's job? That it's sanitizing something?

    Let's cut to the chase. If you smell it more than usual, would that be indication that someone peed in the pool?
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    Re: Chlorine smell questions

    Chem geek, thanks for the clarification. I always know know you will come back with data to back it up. My sniffer does not work like it use too but doesn't bleach have a more sweet smell. Also back to the OP and public pools with "bad pool smell". I would think a lot has to come from the fact that public pools have a higher load and they are bound by a set of rules that TFP sees as below the minimum.
    17500 gallon Doughboy AGP, Hayward DE filter, waiting for the 1.5hp DB pump to go out.
    Learn to take the advice here and be trouble free or use the pool store's advice. "You can't do both and get very far"

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    Re: Chlorine smell questions

    If someone over chlorinated, it will surely smell. My SIL uses pool store methods and you can smell the chlorine in their suits a good 10 feet away sometimes. My suits, TFP method, no smell present. Much as I have wanted to, I haven't tested her water. She uses her strips and is quite pleased with the results so far.....
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    Re: Chlorine smell questions

    More concentrated chlorine might smell a bit different than dilute chlorine, but I wouldn't call it sweet, though it's got a fresh clean sort of scent though that may just be psychological knowing it's bleach. "Bad pool smell" from the chloramines is different and less pleasant while nitrogen trichloride (trichloramine) is downright irritating and very volatile.

    Yes, shocking when there are organics (including algae) in the pool can outgas chloramines and that means its working and when done oxidizing you are left with mostly chlorine so doesn't smell as bad or possibly as much.

    As for knowing if someone pee'd in the pool, you'd more likely detect that by noticing a higher than usual chlorine demand and/or some CC though that doesn't last very long. See Unusual Chlorine Demand -- Peeing in the Pool for a personal experience.
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    peterdaly's Avatar
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    Re: Chlorine smell questions

    Thanks chem geek. I did just have unusually high chlorine demand, right along with the smell complaints.
    Fayetteville, NY -17K gal, IG vinyl, Hayward SP2300VSP Max-Flo Variable Speed Pump, FlowVis Flow Meter, Sand filter
    Self designed Arduino powered automation for pump and solar control, Solar Attic Pool Heater, AutoPilot Digital SWG, TF100

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    Re: Chlorine smell questions

    My Indoor pool smells of chlorine/Bromine when:
    1) it's cloudy water or fighting something
    2) clear water but high bather load I.e. swim meet warm up

    Either way proper ventilation takes care of both.
    Thanks TFP
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