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Thread: Using Calcium Hypochlorite to shock pool

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    Using Calcium Hypochlorite to shock pool

    I just used 4# of calcium hypochlorite to shock my pool, as I have developed mustard algae thanks to the rain floods in Texas. I should be reading about 25 ppm of chlorine, but my Taylor test kit shows almost no chlorine! It dropped my pH from 7.8 to 7.2. Why donít I register chlorine with the test kit?

    19,000 gal in-ground plaster pool; plaster older than 10 years
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    Isaac-1's Avatar
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    Re: Using Calcium Hypochlorite to shock pool

    Which test kit do you have?

    If it is the K-2005 the DPD chlorine test will bleach out at high levels, this is why we do not suggest it, instead the K-2006 has the FAS-DPD chlorine test which will read high level of Chlorine
    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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    Re: Using Calcium Hypochlorite to shock pool

    I’m using K2006 with the DPD test, and I have read chlorine levels in the upper 20s before with no problem.
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    JasonLion's Avatar
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    Re: Using Calcium Hypochlorite to shock pool

    Chlorine is constantly being lost, to sunlight, to algae, to other contaminates in the pool. So you need to be constantly raising it back up.

    If you post a full set of water test results we can give you much more specific advice.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Using Calcium Hypochlorite to shock pool

    Quote Originally Posted by JasonLion View Post
    Chlorine is constantly being lost, to sunlight, to algae, to other contaminates in the pool. So you need to be constantly raising it back up.

    If you post a full set of water test results we can give you much more specific advice.
    I will run a full set tomorrow, but I added 4 pounds of 73% sodium hypochlorite at sundown and an hour later I got almost no pink when I used the DPD powder. Something is strange. My issue has nothing to do with sunlight loss. Iíll post a full set of reading tomorrow.
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    Mod Squad tim5055's Avatar
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    Re: Using Calcium Hypochlorite to shock pool

    If you have that much chlorine demand it's time to SLAM the pool.

    Pool School - SLAM - Shock Level And Maintain
    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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    JasonLion's Avatar
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    Re: Using Calcium Hypochlorite to shock pool

    If you have a full algae bloom or an ammonia problem then losing all of your chlorine is to be expected.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Using Calcium Hypochlorite to shock pool

    Quote Originally Posted by JasonLion View Post
    If you have a full algae bloom or an ammonia problem then losing all of your chlorine is to be expected.
    OK. Here is what I did. I did have mustard algae on the sides of the pool but the water was clear ... no green algae visible in the water. I was coming out of the winter with the pool and had periodically added chlorine bleach to keep some chlorine in the pool until I was ready to balance it for swimming. So, since my cyanuric acid was almost zero, I decided to use some pucks from the pool store. While there I picked up some packs of calcium hypochlorite to shock the pool (normally I shock with liquid bleach) and a bottle of diammonium sulfate that is supposed to kill yellow algae. I followed the instructions and sprinkled the algae stuff around the perimeter, followed by 4# + 1 gallon of 8% bleach.

    An hour after running the pool I was amazed to see no chlorine present in the pool. It ran all night and here are this morningís numbers:

    chlorine - 0
    pH - 7.4
    Total alkalinity - 40
    calcium hardness - 300
    cyanuric acide - about 50-55

    Iím thinking of now going back to the bleach shock treatment, and add enough bleach to bring the pool to 22 ppm chlorine.
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    Mod Squad tim5055's Avatar
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    Re: Using Calcium Hypochlorite to shock pool

    Read the directions on SLAMing your pool in the How To section of Pool School and follow that procedure completely to the end. No more magic potions form the pool store.




    • CC is 0.5 or lower;
    • You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less);
    • And the water is clear.


    When all three are true, then follow the additional directions for Mustard Algae.
    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: Using Calcium Hypochlorite to shock pool

    It looks like the stuff you added to kill the mustard algae may have added ammonia to your pool, which will eat up CL big time.
    20k IG vinyl liner/Aqua Rite SWCG, T-15 cell/Hayward Pro Grid 6020 DE filter/Polaris 280 with booster pump/Hayward Superpump 1 hp/city water/pool installed March 2004

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    Re: Using Calcium Hypochlorite to shock pool

    I don't know, but I would think the Sulfate could act as a Chlorine Scavenger. Does your kit have the FAS/DPD FC/CC test? If so what was your CC level?
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    Re: Using Calcium Hypochlorite to shock pool

    Quote Originally Posted by Patrick_B View Post
    I don't know, but I would think the Sulfate could act as a Chlorine Scavenger. Does your kit have the FAS/DPD FC/CC test? If so what was your CC level?
    Almost none. 0.5 CC.
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    Mod Squad zea3's Avatar
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    Re: Using Calcium Hypochlorite to shock pool

    Diammonium sulfate, sold as Yellow Out, creates an extreme chlorine demand. Read more about it here .
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    Re: Using Calcium Hypochlorite to shock pool

    Pool_dufus

    TFPC tenant - Never put chemistry in your pool when you do not know the outcome

    TFPC Tenant - Pool Stores can and will sell you most anything....whether it helps or hurts your pool.....they just don't know any better

    Logic would then encourage us to stay out of pool stores if we want to manage our water via TFPC.

    That may come across as being kind of a you-know-what, but it is factual and advice we teach every day. We must not be emphasizing it enough.
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    Re: Using Calcium Hypochlorite to shock pool

    The CYA dropping to zero points to an ammonia conversion ... Which equates to high FC demand.

    Plus sounds like the products you added also result in a high FC demand.

    Time to start SLAMing with bleach, and lots of it to remove the chlorine demand.
    Jason, TFP Moderator
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    Re: Using Calcium Hypochlorite to shock pool

    Quote Originally Posted by jblizzle View Post
    The CYA dropping to zero points to an ammonia conversion ... Which equates to high FC demand.

    Plus sounds like the products you added also result in a high FC demand.

    Time to start SLAMing with bleach, and lots of it to remove the chlorine demand.
    Yes, it was the Yellow Out compound that caused my problems. I have now added bleach and gotten my CL level back up into the 20s. With the constant tropical downpours we are having its going to be difficult to hold the shock level up, but I already can see come effects on the yellow algae. Thanks to everyone for their comments. I have learned my lesson. Stay out of the pool store!!
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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