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Thread: very high FC

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    mishkin's Avatar
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    very high FC

    Hi, I just bought TF100 test kit and confused with results. The water looks very clean and I do chlorine does not smell that bad, so I wondering what's going.

    I just bought a house and pool maintenance was new to me. First 4 weeks, I would go every 3-4 days to a local pool store for tests and every time they would say my FC is 5ppm and said to keep it that way. All other parameters were okay. They told me to shock it once a week and keep adding tablets to chlorination which I did. Now when I got TF100 and measured FC, i got 38ppm two days ago and just tested it again and got 41ppm. I am bit confused as well because the laminated instruction in the kit says to multiple number of drops by 0.05 but the examples says if you do 14 drops multiple it by 0.5 which means it would be 7ppm. So is it 0.05 or 0.5?

    Here is my test results:

    2 days ago:
    FC 38ppm ( 76 drops)
    CC 0
    TC 38
    TA 110ppm
    CA 260
    CYA 85
    PH 7.5

    today:
    FC 41ppm ( 82 drops)
    CC 0
    TC 38
    TA 110
    CA 260
    CYA 85
    PH 7.5

    Now i wonder if my pool is even safe to swim. Looks like a crazy level for FC, no?
    11,9k IG gunite pool, Hayward C1200 cartridge filter, Hayward pump with UST1152 motor, Hayward CL220 chlorinator, solar panels, Hayward Navigator Pro vacuum, TF-100 w/ SpeedStir

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    Mod Squad zea3's Avatar
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    Re: very high FC

    Hi, welcome to TFP! There is a typo in the instructions. It should read .5 What size water sample are you using, 10 ml or 25 ml? What have you been using to "shock" and how much have you been using?
    TFP Moderator
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    mishkin's Avatar
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    Re: very high FC

    Quote Originally Posted by zea3
    Hi, welcome to TFP! There is a typo in the instructions. It should read .5 What size water sample are you using, 10 ml or 25 ml? What have you been using to "shock" and how much have you been using?
    thanks for the quick reply! the sample was 10ml as stated in instructions. I used liquid chlorine from a pool store which i think 10.5% and I used about 1.25 gl once a week and trichlor tablets loaded to chlorinator.

    So if it is 0.5, when my FC is crazy high. I am worried now as I have 4 year old kid. Is it safe to swim? should I just wait and do nothing till FC gets down to 4-5? So upset that the store guys said that it was 5ppm and it is totally normal! good thing i bought the kit
    11,9k IG gunite pool, Hayward C1200 cartridge filter, Hayward pump with UST1152 motor, Hayward CL220 chlorinator, solar panels, Hayward Navigator Pro vacuum, TF-100 w/ SpeedStir

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    Re: very high FC

    You are safe to swim below shock level, so wait until your FC comes down to the low 20s.
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
    The most important article on this site - The ABCs of Pool Water Chemistry

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    mishkin's Avatar
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    Re: very high FC

    Quote Originally Posted by Smykowski
    You are safe to swim below shock level, so wait until your FC comes down to the low 20s.
    thanks but still confused..should I look at this chart?
    pool-school/chlorine_cya_chart_shock

    and based on this I should target to FC between 6 and 9 right? where did 20 came from? should I do anything about high FC or just wait? it is very hot here now in 90sF
    11,9k IG gunite pool, Hayward C1200 cartridge filter, Hayward pump with UST1152 motor, Hayward CL220 chlorinator, solar panels, Hayward Navigator Pro vacuum, TF-100 w/ SpeedStir

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    Mod Squad zea3's Avatar
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    Re: very high FC

    Most pool stores use the test that only goes up to 5 ppm, however the color should have been different enough for them to know it may be higher than 5 ppm and inform you of that possibility.

    Using the Pool calculator your recommended FC level is 7-12 ppm with a shock level of 22 ppm. You also have high CYA at 85. Recommended CYA level is 30-50. If you drain and refill 50% of the volume of the pool that will lower your CYA to the correct range and dilute your high FC. You should remove the tabs from the chlorine feeder and not use them anymore. They are contributing to the high levels of FC and CYA.

    We consider a pool safe to swim in up to shock levels. Your pool FC is higher than shock level, so at this point you have 3 choices.
    1. You can remove the tablets and allow the FC to drop on its own. This will take several days, possibly more than a week, and it won't fix the CYA problem.
    2. You can drain to correct the high CYA and lower the FC at the same time. You will have to re-test the FC after re-filling to see if the FC is low enough, but I am pretty sure it will bring the pool below shock level. Depending on your water pressure this may take a day or two, and you will need to re-test and balance the pool as needed when completed.
    3. You can leave the CYA as is and purchase a chlorine remover to lower the FC. This will be quickest way to lower FC, but does nothing about the high CYA.

    In all cases remove the tablets from the chlorinator and don't use them for now. You can let the ones from the chlorinator dry out and save them or you can tie them up in a plastic bag and throw them away.
    TFP Moderator
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    Re: very high FC

    Quote Originally Posted by mishkin
    Quote Originally Posted by Smykowski
    You are safe to swim below shock level, so wait until your FC comes down to the low 20s.
    thanks but still confused..should I look at this chart?
    pool-school/chlorine_cya_chart_shock

    and based on this I should target to FC between 6 and 9 right? where did 20 came from? should I do anything about high FC or just wait? it is very hot here now in 90sF
    Yes, maintenance target is between 6 and 9. Shock value for your CYA level of 85 is between 22 (Pool Calculator) and 33 (Chlorine/CYA chart). I just split the difference for mid-20s.

    That said, let's make sure you understand what's going on here (all of the following is also explained in Pool School). CYA stabilizes FC from sunlight and slows its breakdown. However, it also reduces the sanitizing/oxidizing power of that FC. The higher your CYA, the higher the FC must be to do the same amount of work. "Shock level" is the value used to clear a dirty pool. The 6-9 you are looking at is maintenance levels, which are for already clean pools. At TFP, we use shock level (for a given CYA level) as a safe maximum for swimming, and as a gauge to prevent damage to liners/equipment.

    Bottom line, wait until FC gets to the 20s before you get in to swim. The water will be less irritating to eyes/skin/hair/swimsuits. You can let it fall all the way to maintenance level, but never, ever let it drop below 6.
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
    The most important article on this site - The ABCs of Pool Water Chemistry

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    mishkin's Avatar
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    Re: very high FC

    this is very helpful, thank you both for the explanation!
    11,9k IG gunite pool, Hayward C1200 cartridge filter, Hayward pump with UST1152 motor, Hayward CL220 chlorinator, solar panels, Hayward Navigator Pro vacuum, TF-100 w/ SpeedStir

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