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Thread: Low (0) Chlorine Levels

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    Low (0) Chlorine Levels

    I moved into my first pool 3 weeks ago, and have been trying to get chlorine levels up using pucks and shock. Like most people here, I started at the dreaded pool store, blew a bunch of time and money, and still had 0 chlorine in the pool. They told me I might need to put up to 50 lbs. of shock (at $5/lb) to get the chlorine levels up. So I started researching online and found TFP. After reading a bunch of the posts on here, I ordered a good test kit (Taylor) and decided to follow some of the advice on this site.

    I got my kit yesterday, here are my first readings:
    FC= 0.2
    CC = 0.4
    PH = 7.6 (started at 7.2, but I brought it up with some soda ash)
    CYA = 50

    Using the Chlorine/CYA chart, it looks like I need to get my FC to 20 for shock level, which, according to Pool Math is about 1000 oz. of 8.25 bleach. Being new to this, dumping that much bleach in my pool makes me nervous, so last night I put about half that much in - 484 oz, which should have brought the FC up to about 10 (it was too late to stay up and test again).

    I took a reading again this morning and got this:
    FC = 10.4
    CC = 1.5
    PH = 7.6
    CYA = 50

    So I got the FC up as expected and it held overnight! CC also came up quite a bit. Anybody have any advice? Seems like I might not have to follow the SLAM procedure, but I'm not sure. How do I lower the CC back to 0? Should I try to get my CYA levels down or is 50 acceptable?
    18x36 IG vinyl liner. 29,000 gallons (estimate based on 18x36, 8.5 feet in deep end). Hayward pump, sand filter and heater.

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    Texas Splash's Avatar
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    Re: Low (0) Chlorine Levels

    Good morning and welcome! You are correct! The high CC reading indicates you need to SLAM. I have a SLAM link below, but essentially here's the scoop:
    SLAM is the term used when we “Shock” our pool to a higher “Level” of Free Chlorine (FC) and “Maintain” it that way until 3 objectives are met:
    1. Water is clear
    2. You do not lose any more than 1ppm of FC overnight (that's the OCLT)
    3. CC (Combined Chlorine) is <.5
    ** You MUST meet ALL 3 items above to properly do a SLAM. Simply “spiking" the FC higher than normal isn't SLAMming, therefore there’s a good chance your algae will return.

    To prepare for a SLAM, you should do the following:
    - Adjust PH to 7.2 - 7.5; don’t worry about it after that during the SLAM
    - Ideal CYA should be 30; the higher the CYA, the more bleach required
    - Have a good amount of “regular” liquid bleach on-hand to keep your FC high at all times

    Use the Chlorine/CYA chart (link in my sig) to bring your FC up to the proper SLAM level rating based on your current CYA and make sure it stays there (MAINTAIN) until you meet ALL 3 criteria listed above! That may take just a few days or even a week or two! That is absolutely critical for success.

    At the same time, continue to run your pump 24/7. Remove any “muck” and debris, scrub all parts of your pool to expose any algae, and vacuum/clean (or backwash) filter as necessary. You may have to do this several times. It's a lot of babysitting, but with patience and consistency, you will succeed.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Mod Squad tim5055's Avatar
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    Re: Low (0) Chlorine Levels

    Follow the SLAM. As you did not test to verify the starting FC, it's not a true OCLT. Plus, with CC of 1.5 something is going on in that water, killing algae I'm sure.

    Get it up to shock level and hold it there until all three criteria are met:

    Pass OCLT
    CC less than .5
    Water is clear, which includes not seeing any live/dead algae

    Stic with it no you will have a wonderful swim season. Stop,early and the problems come back time and again.
    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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    Texas Splash's Avatar
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    Re: Low (0) Chlorine Levels

    You are correct that for a CYA of 50, your SLAM FC level is 20, so you need to keep it there - MAINTAIN! Very important. Over time as you SLAM, eventually the free chlorine will win the battle over the organic matter in your pool and your CC level will drop. As noted above, that's one of the requirements to pass the SLAM. Continue to use the Poolmath calculator to adjust your bleach intake, and let us know if you have any questions.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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    Isaac-1's Avatar
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    Re: Low (0) Chlorine Levels

    Like they all said it is time to follow the SLAM process, with luck it will only take a couple of days, as to the CYA of 50, it is a little high, but not too bad, so don't worry about it, just stay away from that stabilized chlorine and it should come down soon enough through regular backwashing, splash out, etc.
    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
    I use and endorse TFtestKits TF-100 from http://tftestkits.net
    ~Remember TFP counts on your donations to keep this site ad free~

  6. Back To Top    #6

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    Re: Low (0) Chlorine Levels

    OK - I added a bunch of bleach at 9:30 AM, retested at 2:30 PM:

    FC = 21.5
    CC = 1.5
    PH = 7.8
    TA = 150

    From what I understand, I need to lower my PH with muriatic acid. Can I do that during the SLAM process or do I need to wait?
    18x36 IG vinyl liner. 29,000 gallons (estimate based on 18x36, 8.5 feet in deep end). Hayward pump, sand filter and heater.

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    Mod Squad tim5055's Avatar
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    Re: Low (0) Chlorine Levels

    You,should have done that before adding the chlorine. Once FC is above 10 the pH reading is inaccurate so you can't trust it to adjust.
    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: Low (0) Chlorine Levels

    Being a new pool owner that battled constant loss of chlorine, thank God I found this site. There's a lot of info on the forum that helped me get my pool back in shape and saved me tons of money by staying out of the pool stores. Heed the advice of the members, follow SLAM instructions and don't get frustrated and give up as it's a process, I almost did. Now the only problem I have is adjusting my pump run time and SWG% as my chlorine level is still high after a successful SLAM.
    Built March 2015 13000 gallon free form exposed aggregate with sheer descent, Jandy 2HP VSP, Jandy 1400 SWG with Aqualink PDA and AquaCal electrical heater. Pentair Clean and Clear filter 150SF. TF100 test kit. Pentair Kreepy Krualy Great White.

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    Re: Low (0) Chlorine Levels

    PH = 7.8
    I need to lower my PH with muriatic acid
    Don't worry about fixing pH during the SLAM process. It's not an accurate read with the chlorine levels being high.

    Good luck!
    22,000 gal 16x34, IG, vinyl (7/14)
    DE Hayward Perflex extended cycle
    Hayward Super Pump
    Aquacal heat pump
    TF-100 test kit

  10. Back To Top    #10

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    Re: Low (0) Chlorine Levels

    Thank you all for your help (in answering my questions and others - I have learned a lot on this site).

    Last night my chlorine measurements were:
    FC=16
    CC=1

    And this morning,
    FC=15.5
    CC=0.5 (or less).

    Can I start to let my chlorine come down to normal levels now, or should I keep them at shock level for another day?
    18x36 IG vinyl liner. 29,000 gallons (estimate based on 18x36, 8.5 feet in deep end). Hayward pump, sand filter and heater.

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    Texas Splash's Avatar
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    Re: Low (0) Chlorine Levels

    If your water is also clear, then YES! You've passed all 3 SLAM requirements. Great job GR! Just remember to always keep that FC at your target level now.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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