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Thread: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

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    Mark R's Avatar
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    Question Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    5 days ago my T-100 test kit had my FC at about 11 and today it was at close to 2.
    CYA is at 60 now which should be good for the rest of the year.
    I brought it up to 11 because we were going to have a pool party and I thought the bathing load would need a little extra.

    My CC is at 0, so no organic problems and the water is crystal clear.

    If I understand the CYA chart the minimum FC should be 5 and target should be 7. My pool has been on the solar for about 10 days and the water temp is at 80 degrees and it has been very sunny and warm outside, 90 degrees today and a bit lower the last few days. Can I expect this quick of a drop for the rest of the summer in FC in a short time? Does the sun really deplete it that quickly ?!?

    If it does, I can expect to use about 3 or more gallons of 8.25% of bleach every week. And maybe more when the air temp hits 100 or more for around 90 straight days soon. I'm shocked how fast the sun can deplete the sanitizer. Also, the warmer the water the faster the bleach is used up ?

    I'm I right in my thinking ?

    Thank you for all your help this year so far

    PH is constantly rising up to 8
    TA is around 100-110
    12k gal Gunite/Hayward filter C5520BH with quad 33 inch filters. 2.5 hp motor. Pool is on south side, so full sun light. Spill over spa.
    Laar's heater LT250-Low NOx Gas Fired for pool/spa 250,000 BTU. Roof mount 6 panel solar system installed east/south. TF-100 test kit. May-September 100+ degrees out side.

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    Mod Squad jblizzle's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    You need to be testing and adding bleach everyday. Hopefully algae has not stated since let the drop too low.

    The higher you raise the FC, the more you will lose to the sun.

    Your thinking is right. The more intense the sun and the warmer the water, the more FC will be consumed.
    Jason, TFP Moderator
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    pwrstrk's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    If you went from 11 to 2 ppm FC in five days with out adding any bleach that's not losing all that much per day, if that's what you are saying.
    Yes you need to add bleach everyday and test more often. For your CYA level, I would be targeting an FC level of 9 and not letting it fall below 5. That will allow for burn off and you won't fall below your min FC level.
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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    Mark R's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    Ok, thank you. The temp of water and outside just shot up pretty fast over the last week. I'll keep up on the FC a little better. I was just shocked how fast the FC went down in such a short time. I need to stock up on bleach then. I found 10% at the pool store for a fairly good price.

    Thank you for the fast replies
    12k gal Gunite/Hayward filter C5520BH with quad 33 inch filters. 2.5 hp motor. Pool is on south side, so full sun light. Spill over spa.
    Laar's heater LT250-Low NOx Gas Fired for pool/spa 250,000 BTU. Roof mount 6 panel solar system installed east/south. TF-100 test kit. May-September 100+ degrees out side.

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    Patrick_B's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    Yep, stay with the frequent testing and adding chlorine until you can predict your test results with surprising accuracy. Don't let that FC fall, or you will get into trouble for sure. Everything sounds like normal loss based on what you said.
    TFP Moderator
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    Isaac-1's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    One more thing here lack of measurable CC does not mean you don't have something growing in your pool. The better test if you suspect increased FC demand is an overnight chlorine loss test. For example you may have algae growing in a poor circulation area (inside a light niche, or under a step), this can increase your chlorine consumption, while the chlorine level in the bulk of the pool water still provides full oxidation and therefore no noticeable increase in CC.
    Indoor 20x40 35,000 gallon vinyl pool with 1.5 HP 2 speed Jandy FloPro pump, Hayward EC75 Perflex DE filter, 11 4x12 Techno-Solis solar panels w/ Aquasolar controller, Aquabot Turbo T Robot Cleaner. Also LMI metering chlorine dispenser pump and HotSpring Jetsetter
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    Mod Squad jblizzle's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    FYI, I found my FC to be a little low yesterday (admittedly I had not tested in over a week assuming the SWG was doing as it should). I have a higher % output than last year, so surprised the FC low. So, last night I used bleach to raise the FC to 19 and shut off the SWG and left the pump on. This morning tested the FC and got 18.5 so passed the OCLT making the low FC not due to something in the water and more likely due to my lower CYA and higher losses the sun.

    Point is, the OCLT is a great sanity check to better understand what is going on in the water and not only useful during the SLAM process.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Richard320's Avatar
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    Re: Hi everyone. Question on Chlorine and the Sun and how fast chlorine is depleted.

    Losing only 9 FC in 5 days is actually pretty darn good! But you're living dangerously letting it drop that low before raising it.

    The pH climbing will slow down if you keep knocking pH down to 7.2 whenever it hits 7.8 because you will also lower TA in the process. Keep ahead of that pH rise, lest you get scaling.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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