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Thread: Strong Chlorine Smell - Spa

  1. #1
    Member bxcrwlly's Avatar
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    Strong Chlorine Smell - Spa

    o.k. so I used the TFP regimen to balance my water. My FC is 5.0 and stabilizer is 70. Ph is 7.5. My spa is connected to the pool via a waterfall but can be isolated for spa only mode when using it. I fired it up Friday night and and the spa started heating. Outside temp was 45 degrees. As the spa heated, as usual, it develops a vapor discharge. The smell had a very strong distinct chlorine odor. I mean really strong. I was worried about breathing this stuff while in the spa. I tested my chlorine thinking maybe I had too much CC and needed to shock the pool; however, that wasn't the case. The FC was 5.0 as noted above and the CC was 0.0.

    I never noticed this strong chlorine odor from the spa when I was keeping my FC around 3.0. Again I wanted to make sure I was following the TFP guidelines.

    Appreciate any insight. Should I be worried about the odor and breathing the fumes? It was a bit disconcerting.
    11,600 gallon plaster salt pool & spa, IC20 SWG, IntelliPH, cartridge filter, 1.5hp Whisper Flow Pump, Gas Heater, Easy Touch System w/remote, 8 roof mounted solar panels

  2. #2
    Senior Member msgtdan's Avatar
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    Re: Strong Chlorine Smell - Spa

    I'm no expert especially on spas but everything I've read or heard says that if you smell chlorine it's CC's though it might not show on a test. I'm not sure if the over night loss test is valid for a spa but I think I'd try it.
    Dan D
    Used 2003 Aqua Leader 27'x52", 17,800 w/10" hopper, SwimPro SW256T 250# sand filter, Hayward PowerFlo LX pump 1hp impellor, Emerson 1 1/2 hp motor, setup Aug 2012 Summer 2011 used Summer Escapes Ring pool 14' x 42", Intex 1600gph sand filter, HTH 6 way test kitTF-100 w/stirrer, Well water @ FC=0, PH=7.2, TA=290, CH=320

  3. #3
    Senior Member DaveNJ's Avatar
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    Re: Strong Chlorine Smell - Spa

    I had noticed this on mine also. I don't think the water circulates from the spa to pool very well. Every so often I turn the valves to empty the spa into the pool, then refill with pool water. Worked for me.
    IG 18x36 oval vinyl, Spill over spa, Northstar 2hp-2spd, 2.5" piping, S310T 500lb Sand filter, 400k gas heater, AutoPilot SWCG
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  4. #4
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    Re: Strong Chlorine Smell - Spa

    This is why at least for standalone spas we recommend targeting an FC of 1-2 ppm before the start of a soak. With a CYA of 30-40 ppm, this usually limits the chlorine and chloramine odors to negligible levels and one then adds chlorine right after their soak to oxidize bather waste.

    The active chlorine level is higher at hotter temperatures at the same FC/CYA ratio. So what works well for your pool to prevent algae growth will be a higher active chlorine level in the spa. Whereas 5 ppm FC with 70 ppm CYA at 84F has an active chlorine level of 0.047 ppm, at 104F it is 0.155 ppm so around 3 times higher. Also, even more importantly, is that the lower FC will form fewer chloramines during the soak as these tend to smell more objectionable.

    So with an attached spa this will be a challenge unless you stop circulation with the pool (i.e. isolate circulation to the spa) and let the chlorine level drop (after you've heated the water up) or you intentionally lower the chlorine level in the spa before you get into it. You can use hydrogen peroxide for this purpose where an equivalent amount of 3% hydrogen peroxide will get rid of the same volume of chlorine as would be added with 6% bleach (so you can use The Pool Calculator to make that calculation).
    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"

  5. #5
    Member bxcrwlly's Avatar
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    Re: Strong Chlorine Smell - Spa

    Chem Geek...thanks. I can and do isolate the spa. I'm curious as to your thoughts with regard to using 3% hydrogen peroxide vs. chlorine neutralizer to reduce the spa chlorine level. In either case, when I turn off the spa isolation returning to the pool "spill-over," I suspect I may need to adjust my pool FC if there is some degradation resulting from the lower FC in the spa?
    11,600 gallon plaster salt pool & spa, IC20 SWG, IntelliPH, cartridge filter, 1.5hp Whisper Flow Pump, Gas Heater, Easy Touch System w/remote, 8 roof mounted solar panels

  6. #6
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    Re: Strong Chlorine Smell - Spa

    You can use a standard chlorine neutralizer if you want to -- hydrogen peroxide is just convenient and only produces oxygen gas and chloride salt.

    The lower FC water mixing with the pool water after your soak should have a very small effect due to the huge differences in volumes of water. If your attached spa is 350 gallons, then having even no chlorine in it and diluting it back to the pool would lower 5 ppm FC down to 5*(11600-350)/11600 = 4.85 ppm FC so a loss of only 0.15 ppm FC.

    Also, your being in a spa at hot temperatures creates roughly double the chlorine demand of your being in a pool for the same amount of time and you normally don't notice the extra chlorine demand in that situation. Every person-hour of soaking in a hot spa (without an ozonator) uses around 9 grams of chlorine so in your 11,600 gallon (43911 liters) pool this would be 9*1000/43911 = 0.2 ppm FC so not very much.

    So between the dilution effect and your bather load, you're looking at 0.35 ppm FC to have to add to the pool.
    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"

  7. #7
    Member bxcrwlly's Avatar
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    Re: Strong Chlorine Smell - Spa

    Chem Geek...thanks so much for the additional detail. I tried your recommendation with Hydrogen Peroxide vs. Neutralizer. The Peroxide worked really fast dropping the FC level between 1-2 within a matter of a few minutes and completely eliminated the strong chlorine odor.
    11,600 gallon plaster salt pool & spa, IC20 SWG, IntelliPH, cartridge filter, 1.5hp Whisper Flow Pump, Gas Heater, Easy Touch System w/remote, 8 roof mounted solar panels

  8. #8

    Re: Strong Chlorine Smell - Spa

    I'm trying to understand, are you using peroxide to accelerating CC oxidation or TC oxidation?
    From reading this forum, I understand that CC is what causes the "chlorine odor", no?
    So, would it be good to use peroxide when odor occurs, then add chlorine to get back up to proper FC level?
    How long will CC take to oxidize without peroxide, or with blower aeration? Yes, I have an ancient spa with an air blower, separate from pool.
    Can you just leave the cover off for an hour or so after chlorinating?
    I hate getting out of the spa and wreaking of chlorine.
    I don't have this issue in my pool.
    24k gallon inground vinyl liner pool, 8'-3' depth, 2 skimmers, 3 returns, basic 5 chem kit.
    Hayward: DE-60 filter, Superpump VS, AquaRite salt chlorinator w/T-Cell 15, TigerShark QC robot. Jacuzzi hot tub ~350gal. Air blower type, w/8 jets.

  9. #9
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    Re: Strong Chlorine Smell - Spa

    The hydrogen peroxide was being used as a chlorine neutralizer to lower the FC level.

    Though the most obnoxious and sensitive odors are caused by some Combined Chlorine (CC), namely some chloramines (mostly dichloramine and especially nitrogen trichloride and only monochloramine if it gets fairly high), you can most certainly smell outgassed hypochlorous acid chlorine as well, though it is harder to detect and is a very faint bleach-like smell. In a properly managed pool as we prescribe on this forum, you'd only smell the chlorine smell if you went to the pool and churned the water or if you had a cover on it and removed it and smelled right away. If you are in the pool for a while, you might not smell it anymore since your nose will get used to it. It also depends on the person -- some have a more sensitive sense of smell. Also, the 5% FC/CYA ratio of saltwater chlorine generator (SWG) pools is a little harder to smell than the 7.5% FC/CYA ratio of the non-SWG pools. In a spa, it's easier to smell the chlorine because the water is hotter so it outgases faster and the active chlorine level is higher (less chlorine is bound to CYA at hotter temperatures).

    When we talk about a properly balanced pool not smelling, we are referring to the obnoxious "pool smell" associated with many commercial/public pools especially indoors. That smell is not pleasant and not what one would call a fresh bleach-like smell.

    As for a spa, after a soak when you add chlorine to oxidize your bather waste it is a good idea to leave the cover off for a while (if you can) so that the volatile disinfection by-products can leave the water and not get trapped under the cover. Otherwise when you open the cover the next time you soak you are more likely to smell these "bad smell" products, though even then you can just leave the cover off for a bit before your soak to handle that. Running the jets for part of the time will also help aerate the water to remove such volatiles. As for how long it takes to oxidize the bather waste, the answer is that it depends since some components get oxidized well within an hour (such as ammonia) while other components take many hours (such as urea) with most in between. In general, with hot spa water most of the bather waste is handled within 24 hours in time for the next soak and the majority of it was handled within 12 hours. What isn't handled just builds up to a level where the rate of introduction from you equals the rate of oxidation of it from the chlorine. I'm sure if you were to measure the water after using the spa for weeks that you would measure some level or urea, but it would be a relatively low amount that is very innocuous -- it isn't volatile (and has no smell) and by itself does not cause any harm (it's used in many skin and hair products) and don't forget that it came from you in the first place as the largest nitrogenous component in both sweat and urine.

    As for your body smelling of chlorine, you can minimize that by targeting 1-2 ppm FC before your soak. That won't be much different that tap water so more like a shower. In a hot spa, the chlorine will combine with ammonia from sweat very quickly forming monochloramine which is the same chemical used in chloramination so may already be in your tap water -- tap water can be chlorinated with chlorine (hypochlorous acid) or chloraminated with monochloramine. You just need to make sure that you dose after your soak in order to prevent bacteria from growing since your bather load will consume all the chlorine or monochloramine. They won't grow much at all in the hour during your soak (worst-case they quadruple in population but in practice they likely won't grow at all due to the chlorine and/or monochloramine during most of the soak) so it's safe to dose right afterwards to kill them off.

    Note that the OP's original issue was noticing a stronger chlorine odor when the FC was 5 compared to when it was 3. So the easiest solution is simply to start off with a lower FC level at the beginning of a soak. The trick is to not go too far and get to zero anytime in between soaks. If the chlorine is too low for too long, then biofilms can form, though as I implied above that doesn't happen in just an hour, but if you go more than 4 hours without chlorine you're at much greater risk, especially 8 hours or more. Once bacteria attach themselves to surfaces and get through their lag phase (sort of like an orientation or adaptation) then they can double in population under ideal conditions every 15-60 minutes. One bacteria can become 65,000 in 4 hours or more than 4 billion in 8 hours. In practice, it's not that extreme, but once a significant amount of bacteria are present they start to form biofilm which are chemicals that protect them and that chlorine does not handle well. If you notice a slimy feel to some spa surfaces, that's possibly biofilm. Even in properly chlorinated spas, it's most commonly found above the water line but there it can be wiped away (a good practice to do whenever you notice it).
    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"

  10. #10

    Re: Strong Chlorine Smell - Spa

    Ok, the original issue was slightly cloudy water with a TC of ~ 0.5-1.0. I'm guessing 300-400gal hot tub.
    So, I added about 1.5 cups of 8.2% bleach. Now my TC is off the chart, OTO test is dark orange/brown with the first drop. Whoops, guess I should have done 1/2 cup.
    Should I leave the cover off and aerate, or use some H2O2?
    24k gallon inground vinyl liner pool, 8'-3' depth, 2 skimmers, 3 returns, basic 5 chem kit.
    Hayward: DE-60 filter, Superpump VS, AquaRite salt chlorinator w/T-Cell 15, TigerShark QC robot. Jacuzzi hot tub ~350gal. Air blower type, w/8 jets.

  11. #11
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    Re: Strong Chlorine Smell - Spa

    You didn't list the size of your spa, but if that 1.5 cups of 8.25% bleach was in 350 gallons, then that is 23 ppm FC and since your water was slightly cloudy why don't you leave the cover off and aerate some. If you retest, the FC will still probably be high so you can then use 3% hydrogen peroxide to lower it where the volume is the same as that of 6% bleach. So to drop the chlorine level by 10 ppm FC you'd use 7-1/4 fluid ounces (about a cup) of 3% hydrogen peroxide.
    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"

  12. #12

    Re: Strong Chlorine Smell - Spa

    Thanks for the help.

    That will not be damaging to skin? Or will they just neutralize one another?
    24k gallon inground vinyl liner pool, 8'-3' depth, 2 skimmers, 3 returns, basic 5 chem kit.
    Hayward: DE-60 filter, Superpump VS, AquaRite salt chlorinator w/T-Cell 15, TigerShark QC robot. Jacuzzi hot tub ~350gal. Air blower type, w/8 jets.

  13. #13
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    Re: Strong Chlorine Smell - Spa

    They neutralize each other.

    HOCl + H2O2 ---> H2O + O2(g) + H+ + Cl-
    Hypochlorous Acid (chlorine) + Hydrogen Peroxide ---> Water + Oxygen Gas + Hydrogen Ion + Chloride Ion

    As is always the case, the addition of chlorinating liquid or bleach raises the pH while the consumption of chlorine lowers the pH. So the hydrogen peroxide will be gone (if you don't add more than needed to neutralize the chlorine) and the chlorine level will be lowered. Other than the drop in pH, some oxygen gas is produced and chloride ion (salt).
    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"

  14. #14

    Re: Strong Chlorine Smell - Spa

    Thank you very much for the help chemgeek.
    The water is crystal clear, so I decided to perform a tranfusion with the pool to dilute the FC level, and if needed I can use a little H2O2.
    24k gallon inground vinyl liner pool, 8'-3' depth, 2 skimmers, 3 returns, basic 5 chem kit.
    Hayward: DE-60 filter, Superpump VS, AquaRite salt chlorinator w/T-Cell 15, TigerShark QC robot. Jacuzzi hot tub ~350gal. Air blower type, w/8 jets.

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