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Thread: Why is FC falling and pH rising with no CC or change in CYA

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    Why is FC falling and pH rising with no CC or change in CYA

    26400gal vinyl
    CYA 30
    FC 3.5
    CC 0
    TA 190
    pH 7.4

    I thought I had mustard algae and slammed. But my FC wouldn't hold and CC continued to read at 0. My pH goes up every day, I've had it at 8 and higher for the last 3 days, add MA to drop it and it goes back up. And, I did have consistent CYA of 50 and we've been hit with some rain. That's when I noticed what I thought was mustard algae so I checked CYA and it was 0! So I got CYA up and started slamming. But something's not right. If it were algae there would be concentrated chlorine killing it, but there's not. Please help

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    Mod Squad tim5055's Avatar
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    Re: Why is FC falling and pH rising with no CC or change in CYA

    First, you have to keep all your post together in one thread. You have started or posted comments/questions on at least 3 different threads that I see. It is extremely difficult to keep up with what you are doing when it is all over the board (no pun intended). You came here for help and the folks here do want to help. But, they need to see the whole picture.

    Now, ignore pH during a SLAM. pH testing reads high when FC is above 10.

    A SLAM is a marathon, not a sprint. You will continually add chlorine, it will keep going down as you oxidize organics in the water.
    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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    Butterfly's Avatar
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    Re: Why is FC falling and pH rising with no CC or change in CYA

    Quote Originally Posted by aek511 View Post
    26400gal vinyl
    CYA 30
    FC 3.5
    CC 0
    TA 190
    pH 7.4

    I thought I had mustard algae and slammed. But my FC wouldn't hold and CC continued to read at 0. My pH goes up every day, I've had it at 8 and higher for the last 3 days, add MA to drop it and it goes back up. And, I did have consistent CYA of 50 and we've been hit with some rain. That's when I noticed what I thought was mustard algae so I checked CYA and it was 0! So I got CYA up and started slamming. But something's not right. If it were algae there would be concentrated chlorine killing it, but there's not. Please help

    You need to finish the SLAM. Don't stop until you meet the three criteria that determine you are done. See red lines in my sig.

    Are you adding enough bleach/liquid chlorine to reach SLAM FC level of 12?

    If yes, how often are you testing/adding?

    Are you brushing every nook and cranny daily?

    It would be helpful if you add your pool and equipment specs in your sig.

    yes, as Tim mention mentioned, ignore the pH until you finish the SLAM.
    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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    Re: Why is FC falling and pH rising with no CC or change in CYA

    Sorry about being everywhere. The other comments were when I first opened the pool and i got it under control. So I started a new thread because I'm not 100% sure I am dealing with mustard algae.

    Yes, I'm slamming to 12 and checking and adding liquid bleach as needed. However, FC won't stay at 12 but CC still reads at 0 so where is it going? And I am brushing like a madman. That's why I was wondering if there's something else going on. And get this, my CYA was 30 this morning. It's now less than that this evening.

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    Re: Why is FC falling and pH rising with no CC or change in CYA

    According to this thread, you are using a K-2006 to test.

    The CYA test is dependent on the lighting, it is recommended to do the test in bright indirect sunlight.

    FC won't stay at 12 because something is consuming it, not all organics cause an increase in CC.

    Also, with regards to this post, I suspect 7.85 is "% available chlorine", you should use "% sodium hypochlorite" (8.25%) for calculations in PoolMath.

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