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Thread: FC did not rise after shock??

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    FC did not rise after shock??

    I did a shock of 710 ounces of bleach to bring FC from 1 to a level of 20. I tested the chlorine 2 hours after shocking and the FC only measured 7. I am using a Taylor test kit. What could be going on?
    18x36 ft
    19,000 gal IG vinyl
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    1HP Whisper Flo Pump

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    Butterfly's Avatar
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    Re: FC did not rise after shock??

    Quote Originally Posted by jmlodin
    I did a shock of 710 ounces of bleach to bring FC from 1 to a level of 20. I tested the chlorine 2 hours after shocking and the FC only measured 7. I am using a Taylor test kit. What could be going on?
    1. The calculated size of your pool (gallons) is incorrect?...or

    2. There are organics in your water that are consuming the chlorine?...or

    3. The bleach has lost it's strength?....or

    3. The test chems are old?...

    4. Incorrect testing technique?...

    I'm just trying to get some ideas out there. How has the testing been going before this?
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

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  3. Back To Top    #3

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    Re: FC did not rise after shock??

    I am sure of the gallons of the pool, the bleach was just purchased today, the test kit is new I just got it today. I am new to this testing, but I think I am doing it right. I am just following the directions. The only thing I was questioning was the water turning pink again after it turned clear. I used the number of drops when it turned clear which is correct I think? The only other factor is the organic material in the pool eating chlorine which is likely. The CC was 3 when I started this process. What do you suggest I do as a next step?
    Thanks so much for your help.
    18x36 ft
    19,000 gal IG vinyl
    Sand filter Tagelus 24"
    1HP Whisper Flo Pump

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    Re: FC did not rise after shock??

    Hi, JM,

    Welcome to the forum.

    The overwhelming probabability is that you have algae in your water and the chlorine is doing exactly what it's supposed to do.....killing the algae. AS it does that, it is also consumed and must be replenished as often as it takes until the depletion stops.

    1. How does your water look?

    2. What is your CYA level?

    3. Can you post full test results for pH, TA, FC, CC, CYA?

    Post back what you can to the above questions. You'll get lot's of great help!
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: FC did not rise after shock??

    We opened the pool a little over a week ago. The water was cloudy and slightly green. We went to Leslies and ended up with a bunch of chemicals and a list of things to do which we finished on Monday. The water has been getting better and better each day but it is not totally clear. I just received my Taylor kit this morning and the results were:
    FC 1
    CC 3
    PH 7.0
    TA 290
    CH 280
    CYA 50

    I shocked the pool this evening and only retested chlorine after 2 hours and the numbers were
    FC 7
    CC 3

    What should I do next?
    18x36 ft
    19,000 gal IG vinyl
    Sand filter Tagelus 24"
    1HP Whisper Flo Pump

  6. Back To Top    #6
    JasonLion's Avatar
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    Re: FC did not rise after shock??

    Add more chlorine. Having a substantial amount of chlorine used up fighting organics in the water is not at all surprising. You need to keep adding chlorine, with pauses to allow it to mix in, till you can maintain shock level.

    Having a substantial organic load when you first open in the spring is not at all surprising. The same thing happens when you have a major algae bloom, the first few chlorine additions get used up very quickly. Add chlorine, give it time to mix in, at least an hour, test again, and repeat as needed until you can hold shock level for more than an hour.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    TizMe's Avatar
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    Re: FC did not rise after shock??

    Where did you purchase your bleach ? The bleach could be out dated. Just because it was bought today doesnt mean it is still good ...

    If your your CC is 3, then as Duraleigh said its going to take A LOT of bleach to get it under control .... until the bleach gets the algae killed off it the algae will consume it (the bleach) sometimes almost as fast as you add it to the water ...
    Les
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    Re: FC did not rise after shock??

    A few more questions....
    It is late here and dark so I will start again in the morning. To determine how much bleach to add each time I recheck FC, would I put my new FC number in the calculator to determine how much bleach to add to get to a shock level of 20 ppm? It is forecast to be 57 degrees here tomorrow with some sun, is that a factor?
    18x36 ft
    19,000 gal IG vinyl
    Sand filter Tagelus 24"
    1HP Whisper Flo Pump

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    Re: FC did not rise after shock??

    JM,

    It's time to enroll you in Pool School. Read as much as you can but, particulary, the "basics of pool water chemistry" and "defeating algae". When you've read all you can, it's sure to bring more questions so post 'em up and you'll get lot's more help!

    You're off to a good start because you have a good test kit.....it'll tell you the status of your water so you'll know what to do next. When you post back, post all your test results......pH, TA, FC, CC, CYA.

    PS - There are no graduates from Pool School....there are no diplomas or degrees. Pool School is the constantly evolving, finest source of pool info that can be found anywhere on the net. Everyone enrolled is a learning student and is expected to share the knowledge he/she gains every chance he gets. Each of us on this forum has been a newbie at one point in time but we are all committed to sharing what we have learned with anyone willing to take the plunge and (mentally) sign up.
    Dave S. - Forum owner
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    Butterfly's Avatar
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    Re: FC did not rise after shock??

    Quote Originally Posted by jmlodin
    A few more questions....
    It is late here and dark so I will start again in the morning. To determine how much bleach to add each time I recheck FC, would I put my new FC number in the calculator to determine how much bleach to add to get to a shock level of 20 ppm?

    Correct.

    It is forecast to be 57 degrees here tomorrow with some sun, is that a factor?

    The sunlight will consume some of your chlorine. You can still shock.
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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