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Thread: Vanishing chlorine

  1. Back To Top    #1
    Daf-Tekno's Avatar
    Join Date
    Sep 2014
    Calgary / AB

    Vanishing chlorine

    Dear TFP,

    I've been operating our tub since autumn 2011, and at first all was well.

    I followed Jacuzzi Calgary's suggested chemical regime:

    Add chlorine when levels get low through the week
    Each weekend, add 'Foundation', 'Shock', 'Super Clarifier' and 'Secure'
    Every other week, add 'Spa Perfect'.
    Adjust for pH / TA as necessary.

    The chlorine level would stay stable, going down slowly over a matter of days.

    Then, they came and fitted a 'Clear-Ray' UV lamp, but removed my ozonator (I was out so I didn't see them do this).

    Ever since, my chlorine just vanishes.
    I get a reading of 0, I add 4 tablespoons of stabilised chlorine, and 24hrs later, it's at 0 again! (No use in between).

    I eventually replaced the 'Clear-Ray' with a Delta UV lamp (much bigger and up to the job) and refitted a new ozonator.
    (The back pressure of the Delta UV seems to be slowing down the ozonator water circuit, so I'm not sure if the venturi is sucking the ozone effectively).

    However, I'm still experiencing the vanishing chlorine.

    I've tried Super-chlorination, then Super-Super-chlorination (suggested by Jacuzzi Calgary), but even using a whole 2kg tub of chlorine made no difference!

    Just how fast is chlorine meant to disappear in a normally-operating tub?

    I've thought of switching to a salt-water chlorine generating system, so I'd never run out of chlorine, but if there's something wrong with my tub, then I feel I should identify it and get it fixed instead of adding another level of complexity that may not fix the issue.

    What could be making my chlorine vanish so quickly?

    Any ideas would be greatly appreciated.
    Thank you.

    Jacuzzi J480 (2007) 1700 litres, ozonator, Delta UV lamp

  2. Back To Top    #2
    CUTiger78's Avatar
    Join Date
    May 2009

    Re: Vanishing chlorine

    Ever change the water in that hot tub? If you haven't, I'll bet the CYA level is unbelievably high and you would have to add a huge amount of chlorine to show any available free chlorine.

    BTW, I bet you would be happy with the SWG system you mentioned and getting rid of all those other chemicals. I never added anything but Cl in mine. I'll defer to a hot tub expert, though.

    Good luck!
    36K gallon 42X22 gunite/plaster kidney-shaped IG;
    1 hp Hayward Super Pump (new in 2012);
    Hayward S244T sand filter w/ Zeosand (both new in 2009);
    175K BTU LAARS Lite2 LG natural gas heater; Polaris 380;
    TF-100 test kit.

  3. Back To Top    #3
    Mod Squad tim5055's Avatar
    Join Date
    May 2014
    Franklin, NC

    Re: Vanishing chlorine

    Ozone depletes/oxidises chlorine. That is why we add CYA to a pool to protect the chlorine. A spa generally does not need a lot of CYA as for the most part it is covered and protected from the UV rays of the sun. You have just added a bigger UV lamp which will deplete the chlorine faster.

    I think you need to eliminate the "chemical regime" as it is really there to move money from your pocket to theirs. Just like my pool I only add to my spa what it needs when it needs it. Generally this is chlorine a little CYA and adjustments to the pH.

    Read How do I use Chlorine in my Spa for more information.
    TFP Moderator

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  4. Back To Top    #4

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Vanishing chlorine

    As noted in Chemistries of Ozone for Municipal Pool and Spa Water Treatment, ozone reacts with chlorine to deplete it to chloride and chlorate. I suspect that your original ozonator had either failed or was weak so you did not have such noticeable depletion, but when they replaced it with a new ozonator it is working or more powerful so now you notice the depletion. As a general rule, in a hot spa not being used (i.e. in between spaced-out soaks) 24-hour Free Chlorine (FC) loss is around 25% per day while with an ozonator it is usually at least 50% per day.

    However, you say you noticed the depletion when the 'Clear-Ray' UV lamp was added so perhaps that is the source of the depletion, but according to this FAQ, "The CLEARRAY™ bulb is a low-pressure 10W UV-C monochromatic bulb." This means it has primarily single wavelength output near 254 nm. The molar absorption coefficient at 254 nm of hypochlorous acid is 59 M-1cm-1 and of hypochlorite ion is 66 M-1cm-1 so a powerful UV system can most certainly deplete chlorine. Adding the ozonator on top of this would simply deplete chlorine even faster.

    It is also possible that some time during these installations that the chlorine went to zero in the spa and biofilms formed. Also, with a new spa there are greases and oils that need to be removed. We recommend using Ahh-Some to remove/dislodge such material. However, I'd suggest you remove both the UV and ozone systems since they will deplete chlorine and are not necessary. The only use for the ozone system would be if you were to use the spa every day or two since it will help to oxidize bather waste, but because it also depletes chlorine you would not want to use one if you only soak once or twice a week.
    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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