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Thread: Disappearing Chlorine

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    Disappearing Chlorine

    Help! I've been using this site as a reference for a couple of years to much success. This year, I cannot seem to keep Chlorine in my pool. Readings are as follows (and have been confirmed with testing at home and at local pool supply store):

    Ph: 7.5
    TA: 100
    Calcium Hardness: 30
    CYA: 30

    I cannot recall the exact readings for the rest of the things the pool store tests for - but they all registered normal.

    At the beginning of the day after adding approx 3 jugs (just under 1 gallon each) of Clorox bleach, the FC and TC are around 3 ppm. By the following morning, the FC and TC will both be 0 ppm. The pool gets 8 hours of sunlight per day and the water temperature currently fluctuates between 87 and 90 degrees Fahrenheit. The pool store said it is because I am using liquid Clorox rather than the granules they sold me in the past. But, I had some granules I bought earlier this year and I added 5 lbs one morning, and the following morning the FC and TC were back to 0. Is this normal? Any suggestions on how to keep the chlorine in the pool?
    In-ground pool, 39,000 gallons, vinyl liner, Hayward 500-lb sand filter, Hayward pump.

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    Mod Squad tim5055's Avatar
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    Re: Disappearing Chlorine

    Welcome to TFP!

    Well, you are using pool store testing and "confirming" it at home? What test kit are you using to confirm it?

    How does,the water look?

    Two things consume chlorine, UV rays of the sun and organics in the water. We just need results we can be sure of to make recommendations.
    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: Disappearing Chlorine

    You will lose around 3ppm, probably more in the summer, to sunlight burn off. You will lose more if you have something growing in the pool.

    As a test, add enough liquid chlorine to your pool after the sun goes down to get your FC level above your target range. Up to 10 or 12. Set your pump to run and let it run all night.

    Measure your FC level 30 minutes after you added the CL. Then, in the morning before the sun hits the pool, retest your FC level. If you lost 1ppm or more of FC overnight, you have something blooming and you'll need to SLAM your pool.

    This is called the Overnight Chlorine Loss Test or OCLT around here for short.

    Liquid chlorine doesn't need to dissolve like granules do, so the FC is available at once. In that sense, it doesn't "last as long" because it doesn't take hours to dissolve into the water. But CL is CL, and however it gets into the pool, it will be lost at the same rate.
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    Mod Squad jblizzle's Avatar
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    Re: Disappearing Chlorine

    Welcome to TFP!!!

    Please add a more useful location (City, State or City, Country) to your profile as described HERE as it will help us help you ... no idea where Lilburn is

    Forget the pool store testing. What test kit are YOU using and what are YOUR results?

    Only 2 things consume chlorine, the sun and organics in the water. If you are losing it all over night, then clearly there is something in the water and you will need to follow the ShockLevelAndMAINTAIN Process to eliminate it. And to do that, you will need the FAS-DPD chlorine test included in the Recommended Test Kits.
    Jason, TFP Moderator
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    Re: Disappearing Chlorine

    Thanks, Tim! The test kit is Leslie's Total Poolcare Test Kit per the sticker on the box, but all the reagents inside the kit are Taylor brand. The pool looks great - crystal clear, no issue with algae at all this year. We (four people) are swimming in it daily and more people (closer to 10-12) on the weekends.
    In-ground pool, 39,000 gallons, vinyl liner, Hayward 500-lb sand filter, Hayward pump.

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    Re: Disappearing Chlorine

    Any suggestions if I cannot run the pump overnight? The pool is surrounded by large oak trees that drop bundles of leaves into the pool, clogging the basket and spiking the pressure dangerously high when not monitored. It's not a problem during the day, as I empty the basket 2-3 times, but would be an issue overnight.
    In-ground pool, 39,000 gallons, vinyl liner, Hayward 500-lb sand filter, Hayward pump.

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    Mod Squad tim5055's Avatar
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    Re: Disappearing Chlorine

    I'm going to guess you are just outside Hotlanta so you will loose a lot to the sun, especially if your CYA is 30

    Update your location to add the state like Jason recommended.

    The test kit you have is probably the Leslie's version of the K2005. They push that one hard. It limits you to 10 chlorine and it is a color match if I remember correctly. Kind of hard to do an OCLT because you don't see the exact chlorine level.

    Does your test kit have this test. FAS/DPD Test

    If not, that confirms you have a K2005. And you may want to pick up this individual test.
    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: Disappearing Chlorine

    I am in Lilburn, GA. My results are the same as the store using a Taylor test kit branded as Leslie's Total Poolcare DPD Test Kit.

    I am losing 3 ppm in chlorine in 24 hours. Is this normal?
    In-ground pool, 39,000 gallons, vinyl liner, Hayward 500-lb sand filter, Hayward pump.

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    Mod Squad jblizzle's Avatar
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    Re: Disappearing Chlorine

    Just want to point out that clogging the skimmer with leaves would result in the pressure dropping in the filter, not spiking.

    The low CYA could certainly be part of the problem. But now with the FC dropping so low so often, I would suspect that there is stuff lurking in the water now too. You should to Perform the Overnight Chlorine Loss Test to see if you lose FC overnight ... again, need the FAS-DPD Chlorine Test.

    Yes a 3ppm loss is pretty normal. But you can NOT let the FC drop below the minimum for you CYA as shown in the FC/CYA Chart.
    Jason, TFP Moderator
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    Mod Squad tim5055's Avatar
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    Re: Disappearing Chlorine

    Quote Originally Posted by JennJones View Post
    I am in Lilburn, GA. My results are the same as the store using a Taylor test kit branded as Leslie's Total Poolcare DPD Test Kit.

    I am losing 3 ppm in chlorine in 24 hours. Is this normal?
    3ppm per day would be normal.

    You should have the FAS/DPD test I linked above because it's more exact.
    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: Disappearing Chlorine

    Thanks to everyone. I will pick up that FAS-DPD test and perform the overnight chlorine loss test. Thanks, again!
    In-ground pool, 39,000 gallons, vinyl liner, Hayward 500-lb sand filter, Hayward pump.

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    Mod Squad tim5055's Avatar
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    Re: Disappearing Chlorine

    Quote Originally Posted by JennJones View Post
    Thanks to everyone. I will pick up that FAS-DPD test and perform the overnight chlorine loss test. Thanks, again!
    i doubt you will be able to pick one up. Almost no one stocks them and Leslie's will tell you you don't need it.

    Tftestkits.net is your best bet. While you are at it look at the SpeedStir and the Sample Sizer as both make your testing more accurate and easier.
    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: Disappearing Chlorine

    Quote Originally Posted by tim5055 View Post
    i doubt you will be able to pick one up. Almost no one stocks them and Leslie's will tell you you don't need it.

    Tftestkits.net is your best bet. While you are at it look at the SpeedStir and the Sample Sizer as both make your testing more accurate and easier.
    Will do. Thanks, again.
    In-ground pool, 39,000 gallons, vinyl liner, Hayward 500-lb sand filter, Hayward pump.

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