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Thread: Understanding the Chlorine / CYA Chart

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    essjay75's Avatar
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    Understanding the Chlorine / CYA Chart

    I was just on the Pool School page and researching information about how to SLAM. Below is the FC Shock Level chart that I copied from the Chlorine/Cya Chart:

    Non -SWG Pools

    CYA (Stabilizer) Minimum FC Target FC Shock FC
    20*
    2
    3
    10
    30
    2
    4
    12
    40
    3
    5
    16
    50
    4
    6
    20
    60
    5
    7
    24
    70*
    5
    8
    28
    80*
    6
    9
    31
    90*
    7
    10
    35
    100*
    7
    12
    39


    I'm sorry for being so ignorant but I don't understand what the Shock FC column means. If my CYA is at 40 (for example) but my chlorine is at 1, how much shock to I add to get things balanced?

    Thanks in advance for your help!
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    Mod Squad YippeeSkippy's Avatar
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    Re: Understanding the Chlorine / CYA Chart

    When you have x amount of CYA (stabilizer) in your pool, your chlorine requirements must be of a certain amount to keep the pool healthy. When the pool is sick (algae, gross contamination, cloudy, testing shows CC's,etc) the way to bring the pool back to health is to kill all the cooties with liquid chlorine at a high enough level, i.e. the Shock # on CYA chart, to kill and then maintain that level for as long as the *process* takes. We call this a SLAM procedure, but in the past they called it "Shocking"

    Some pool stores sell a product called "Shock" which might be stabilized chlorine or liquid chlorine or some calcium with chlorine...its a one time toss it in and pray type product. It doesn't work very well and in some instances actually adds to the pool's problems.

    So by reading the CYA/Chlorine chart if your CYA is accurately tested to be 50, you'd want to keep your day to day chlorine around FC 6, but never dropping below FC 4 or algae can get a foot up in the pool. If algae did that you would raise the FC level to 20 for the *entire* time you're cleaning the pool up. 24/7 if possible.

    I hope this helps explain the chart?
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    Mod Squad jblizzle's Avatar
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    Re: Understanding the Chlorine / CYA Chart

    Just to add, after you determine your "Now" FC number and your "Target" FC number (for daily maintenance or for shock level), you would put those numbers into PoolMath to determine how much bleach is required to give the desired change in FC.
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    Re: Understanding the Chlorine / CYA Chart

    FC stands for "free chlorine" - it's a measurement of chlorine level in the water. Units are ppm (parts per million). From the original post, I wasn't sure that was clear to you. So, the shock FC column gives you the level of free chlorine you need to reach, and maintain, during the SLAM process.
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    Re: Understanding the Chlorine / CYA Chart

    We could change the name of the column to "SLAM FC" to be more clear. We've moved away from calling the process shocking your pool because it's not a one-time event and the maintenance of the higher FC level is a key part of the process.
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    Divin Dave's Avatar
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    Re: Understanding the Chlorine / CYA Chart

    I agree with doing this. The word 'shock' means too many different things to too many different people.

    Quote Originally Posted by chem geek View Post
    We could change the name of the column to "SLAM FC" to be more clear. We've moved away from calling the process shocking your pool because it's not a one-time event and the maintenance of the higher FC level is a key part of the process.
    Divin Dave,
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    Mod Squad jblizzle's Avatar
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    Re: Understanding the Chlorine / CYA Chart

    "Shock level" is in the SLAM acronym so I'm not sure it makes sense to change the table.
    Jason, TFP Moderator
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    Re: Understanding the Chlorine / CYA Chart

    Make that SLAM FC a hyperlink to the slam page as well.
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    Re: Understanding the Chlorine / CYA Chart

    Quote Originally Posted by Divin Dave View Post
    I agree with doing this. The word 'shock' means too many different things to too many different people.


    I'd heard many versions of "shocking" a pool. It wasn't until I arrived at this forum that it cleared up for me.
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    Re: Understanding the Chlorine / CYA Chart

    I have noticed that the term "shocking" does cause some confusions. Interesting.


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