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Thread: Shock the pool after replace 2/3 water?

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    Shock the pool after replace 2/3 water?

    In order to reduce CYA, I replaced 2/3 of my pool (in one time) with tap water.

    PoolSchool says "If you have algae, or the CC level is above 0.5, or the free chlorine (FC) level is zero, you should shock the pool. Many people also like to shock the pool when the FC level falls significantly, as it often does after a major storm or large swim party."

    Before replacing water, FC 4-5, CYA 100-110
    After, FC 0, CYA 40-50.
    Then I bring FC up to 5 by Clorox.

    In my case, do I need to shock my pool?
    Another question, suppose I have to shock, after
    "A:CC is 0.5 or lower; B:An overnight FC loss test shows a loss of 1.0 ppm or less; C:And the water is clear."
    is there anything else need to do to lower FC, or just let it go down by itself?

    Thank you

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    Richard320's Avatar
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    Re: Shock the pool after replace 2/3 water?

    I reviewed your other thread. Is the water still clear?

    If so, I'd run it up to shock level for a day, then do the overnight test. If it passes (and it should), you can relax and the chlorine level will drop all by itself when sunlight hits it, probably 2 or 3 ppm per day. It is safe to swim up to shock level, so if the pH is good and the temperature is bearable, have a swim!
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Shock the pool after replace 2/3 water?

    Quote Originally Posted by Richard320
    I reviewed your other thread. Is the water still clear?

    If so, I'd run it up to shock level for a day, then do the overnight test. If it passes (and it should), you can relax and the chlorine level will drop all by itself when sunlight hits it, probably 2 or 3 ppm per day. It is safe to swim up to shock level, so if the pH is good and the temperature is bearable, have a swim!
    Thank you so much for the prompt reply, Richard!

    The water looks quite good (as before )
    Now the FC in my pool is 4.8-5 (after sunset), CC <=0.2 CYA 40-50, PH 8, TA 100, CH 250
    Tomorrow morning, I will do the overnight test. If it pass (<1), do you think I still need to shock my pool?

    Also, I will get some muriatic acid tomorrow to lower the PH.

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    linen's Avatar
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    Re: Shock the pool after replace 2/3 water?

    Just a note...no need to do the 25 ml sample for FC and CC, the 10 ml sample amount will give you enough resolution (0.5 ppm) and will save you reagents.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Shock the pool after replace 2/3 water?

    Quote Originally Posted by linen
    Just a note...no need to do the 25 ml sample for FC and CC, the 10 ml sample amount will give you enough resolution (0.5 ppm) and will save you reagents.
    Even for overnight test? I though overnight test requires fine precision.

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    linen's Avatar
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    Re: Shock the pool after replace 2/3 water?

    0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Shock the pool after replace 2/3 water?

    Quote Originally Posted by linen
    0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.
    Got it. Thank you
    Do I need to shock my pool if OCLT <1ppm?

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    Richard320's Avatar
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    Re: Shock the pool after replace 2/3 water?

    Quote Originally Posted by snuzxj
    Quote Originally Posted by linen
    0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.
    Got it. Thank you
    Do I need to shock my pool if OCLT <1ppm?
    Straight off Linen's signature: 1. CC is less than 0.5 ppm, 2. An OCLT shows a loss of 1.0 ppm or less and, 3. The water is crystal clear.

    If it passes, you're done.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Shock the pool after replace 2/3 water?

    Quote Originally Posted by Richard320
    Quote Originally Posted by snuzxj
    Quote Originally Posted by linen
    0.5 ppm is plenty since you are looking for a OCLT of 1 ppm or less.
    Got it. Thank you
    Do I need to shock my pool if OCLT <1ppm?
    Straight off Linen's signature: 1. CC is less than 0.5 ppm, 2. An OCLT shows a loss of 1.0 ppm or less and, 3. The water is crystal clear.

    If it passes, you're done.
    Sorry, as a newbie, I am a little confused.
    Those 3 criteria are the condition of "stopping" Shocking Process.
    But if my pool meets them before shocking (i.e., low FC), do I still need to "begin" shocking process by raising FC?

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    linen's Avatar
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    Re: Shock the pool after replace 2/3 water?

    Since your water is clear, and your CC<0.5 ppm, then you have no reason to do the shocking process. However given your pools history, as Richard320 said, I too would recommend doing the OCLT, and I would raise you FC up to shock level when doing it...just to be sure.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  11. Back To Top    #11
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    Re: Shock the pool after replace 2/3 water?

    Quote Originally Posted by linen
    Since your water is clear, and your CC<0.5 ppm, then you have no reason to do the shocking process. However given your pools history, I would do the OCLT, and I would raise you FC up to shock level when doing it...just to be sure.
    I see. Thank you, linen

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    duraleigh's Avatar
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    Re: Shock the pool after replace 2/3 water?

    All the discussion about shock has disregarded your one parameter which is out of line. Get your pH down to about 7.5 sooner rather than later.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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