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Thread: UV light rapid free chlorine level dropping

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    UV light rapid free chlorine level dropping

    Could a Trident UV light installed cause a rapid reduction in free chlorine? It seems reasonable given the suns UV light affects on chlorine. As fast I add chlorine it rapidly degrades to zero.FC:0 to.25 CC:0 PH: 7.4 CYA:45 TA: 110 CH: 240 water quality: great clear. Issue can not maintain FC level over any amount of time period (> 3-4 hrs) no matter how many SLAMs and from a cost perspective water replace would be more cost efficient. But is real problem the UV light? It makes sense.
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Mod Squad tim5055's Avatar
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    Re: UV light rapid free chlorine level dropping

    I would look at organics in the water. Did you ever complete your SlAM? THIS thread just went off to nowhere.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: UV light rapid free chlorine level dropping

    Yes I did was asking this question to get feedback on the UV light as a possible cause given the greatest loss is due to the breakdown of chlorine from UV in sunlight:

    2OCl- + --
    ν
    --> O2(g) + 2Cl-
    Hypochlorite Ion --> Oxygen Gas + Chloride Ion

    2HOCl --
    ν
    --> O2(g) + 2H+ + 2Cl-
    Hypochlorous Acid --> Oxygen Gas + Hydrogen Ion + Chloride Ion
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    ranger_ric's Avatar
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    Re: UV light rapid free chlorine level dropping

    Can you turn off the UV light for a day and see if it will then hold chlorine?
    17500 Gal Above Ground, 1.5HP Dynamo Pump, 250# Pentair Sand filter with ZeoLite. Diver Dave Cleaner. TFP test kit w/SpeedStir, 7 Grandaughters and 1 Grandson swimming every week WooooHooo!!

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    Re: UV light rapid free chlorine level dropping

    UV does consume chlorine, but not normally enough for me to call it "a rapid reduction". Typically you might lose 1 ppm per day because of the UV. UV units come in different sizes so that varies, but even a large unit on a small pool isn't going to be more than twice that.
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    Re: UV light rapid free chlorine level dropping

    thanks for the information out max 2ppm per day via UV light. I could not find that data point.
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Re: UV light rapid free chlorine level dropping

    tim after 80gals of NEW 12.5% Chlorine (yes stored properly) slamming and following the TFP process, did not improve FC CC TC ratios… at some point the cost of chlorine and time Vs new water becomes a factor. Next year I will empty and acid wash the surface. all equipment is new. there are small cracks but no leaks in pool plaster surface. I am considering resurfacing pool. age 1994. water is crystal clear but i can not keep FC levels maintained for any period of time. If organics are present they must be an extremely resistant strain or be inhabiting a structural component. The pool gets very little use filter runs 24/7. new cartridges lows pressure…etc all good. there is no apparent introduction of organics. Chlorine breakdown is thru 1 sunlight and 2 bather load and 3 organics..any thoughts welcomed..
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Re: UV light rapid free chlorine level dropping

    What is your cyanuric acid level?

    Is this an indoor pool?

    What is the bather load?

    Why did you add UV?

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    Re: UV light rapid free chlorine level dropping

    james that information is above
    FC:0 to.25 CC:0 PH: 7.4 CYA:45 TA: 110 CH: 240 water quality: great clear.
    in ground pool---outside
    little use 2 bathers once a week.
    added UV in a futile attempt to reduce CC levels
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Re: UV light rapid free chlorine level dropping

    A low use, outdoor, residential pool should not have any appreciable amount of combined chlorine. What CC levels were you getting on your tests?

    Have you used anything like non-chlorine shock?

    Were you maintaining your FC at the correct level for your CYA or did it get too low for a while?

    I would suggest an FC of about 7.5 % of the CYA.

    How are you chlorinating?

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    Re: UV light rapid free chlorine level dropping

    CC level anywhere from 1.5-10ppm during SLAM, process shock cya(30-50) from TFP chart CF(16-20ppm) trying to maintain Fc above 3ppm during 1-2 waiting between SLAMing was unsuccessful. FC loss was significant ,would shorten wait time and shock again to bring Fc to 16-20ppm wait brush,test, wait repeat … after 3-4 days of this I could not maintain Fc for any time period. at some point cost of chlorine and time Vs water replacement is a viable option. water replace cost $700
    96gal of chlorine(12.5%) $6=$600. overnight never maintained Fc levels. FC returns to .5-1ppm. Today FC:.5-1 CC:0-.5 PH: 7.4 CYA:35 TA: 95 CH: 240 water quality: great clear. but if i shock with 3 or 4gal of 12.5% Chlorine FC and CC rise but dissipate would again. at what point water replacement is a cost consideration. Yes prior to TFP use non-chlorine shock--no change could not maintain FC level for any time period. I use liquid chlorine only for shocking and maintain of Fc. I am now looking for why and how organics are present.. pool surface issues, pool light niche, cracks on plaster, ducks(not lately), etc.. bather load not an issue. I have use pro algae 60 2-3 times 1 quart at night brush clean pool filter, shock.. no change Thoughts
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Re: UV light rapid free chlorine level dropping

    This might be a case where bacteria converted cyanuric acid into ammonia. This can create a huge chlorine demand. The Slam will eventually clear whatever is in the water. A partial drain and refill might be worthwhile if it can be done safely.

    Note that non-chlorine shock can show up as CC.

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    Re: UV light rapid free chlorine level dropping

    I will revisit next year
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Re: UV light rapid free chlorine level dropping

    Which Trident system you have? They have multiple bulbs and are sized per flow rate and gallons. I would unplug a bulb and see what happens.

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    Re: UV light rapid free chlorine level dropping

    If you have a 2 lamp or 3 lamp system try unplugging a bulb to see if that could be the case. I've seen UV strong enough to remove 10ppm of shock in 8 hours (Hanovia)

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    Re: UV light rapid free chlorine level dropping

    If you have a 2 bulb or 3 bulb trident unplug a bulb and see if that helps. Trident is sized for flow rate and water temp. If you have too many bulbs lit it could cause the problem you stated.

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    Re: UV light rapid free chlorine level dropping

    If you have a trident series 2 with the S12 or S13 i would unplug a bulb or as another member said just shut it off for a bit. Ive seen commercial UV systems destroy 20# of CAL Hypo in 4 hours. UV works, sometimes too good!

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    Re: UV light rapid free chlorine level dropping

    Something is not right here and maybe more info would help.

    When did you install the UV light? Before or after your slam?
    When did you start having problems with fc holding?
    What led you to slam initially?
    What were you using to sanitize the pool before your slam?
    How could you have completed the slam if your FC did not hold overnight? (See pool school for the complete details of "shocking and maintain" (slam) which include FC not dropping overnight be more than 1)

    From your reports of FC not holding perhaps the UV is contributing but perhaps other factors are exacerbating: eg
    - that polyquat 60 in large amounts can cause an increase in chlorine demand
    - if you were previously using something like baquacil system or hydrogen peroxide to sanitize or shock chlorine is not compatible and "conversion" is required
    - if the pool condition prior to your first slam a few weeks ago was swampy and you have ammonia in your water from cya breakdown, it will take a HUGE amount of chlorine to break it down and make the water hold FC (been there, done that and you have to keep chlorinating without stop til it holds)

    So while removing the UV entirely is a obvious experiment to try, the fact that you got the UV light in response to a problem suggests that the uv light may not really be the problem.

    The more info we have on the circumstances and prior pool maintenance items used, the better the chance we can give meaningful info
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    Re: UV light rapid free chlorine level dropping

    i have the series 2, 3 uv light system I installed it 2 years ago because cc levels were high I thought it may help reduce cc and as backup sanitizer.water is and was alway clear and balanced except for FC CC &TC. I had been having problems with holding FC and rising CC level for last 4-5 years. I only used the pool store for testing. they would always say that your nitrates are high and thats why you can't hold Fc, you need to replace water. I replaced water 3 years ago. and two years before that. always use super pool treat as shock(dichlor) and 3" pucks (trichlor) and pro algae 60 as maintenance. only use non shock once during last attempt with prior water to reduce CC.. didn't work. Pool store again wanted to replace water. So i looked to the internet and found FTP and ordered test TFT test kit. ordered 100 gal new 12.5% liquid chlorine for slam. after 96gal I was unable to hold FC overnight & FC to CC ratio didn't improve. Fc would decrease rapidly 16-20ppm to 3ppm or less in 1 hour. CC would rise to 10ppm. I was not getting anywhere. maybe should have ordered another 100gal of 12.5% chlorine but the cost of winning the war was of consideration. I have one month left of swim time,so I was looking other cases of the organic problem…i.e. surface of pool. I had the trident d/c because to the recall. I will d/c again & try slam again but with chlorine cost & time& other balancing chemical cost water replace must be considered. Thoughts
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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    Re: UV light rapid free chlorine level dropping

    Can you quantify HUGE amounts of chlorine is 100gal Huge? 25,000 gal pool. also last year CYA was high 90-100 to 135, we were using shock Trichlor/dichlor which has CYA in it. On opening this water clear CYA down to 30. ph high so I balanced as shocked pool.
    pool owner 25yrs 25,000 gal plaster inground pool equip: pentair clean & clear Plus CCP42 cartridge filter,pentair whisperflow 1.5H pump, raypak heater r406a ng, trident uv s2-23, polaris 9550 sport pool cleaner

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