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Thread: Normal FC drop overnight?

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    Join Date
    Aug 2007

    Normal FC drop overnight?

    What is considered normal for an overnight FC drop? I am trying to eliminate mustard algae as a problem and tested my water last night and again this morning. I tested last night(more than once) and got 4.5 and 5 in 2 different tests. This morning I am getting 4 and 4.5 in 3 different tests. Looks like I have lost .5ppm FC and possibly up to 1 ppm but not more than 1ppm. I was hoping for no loss at all. Is this drop normal?
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    frustratedpoolmom's Avatar
    Join Date
    May 2007
    SWSuburban Chicago, IL

    Re: Normal FC drop overnight?

    1ppm or less is normal. I don't think it's algae.
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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Normal FC drop overnight?

    Ideally there shouldn't be any overnight drop. But the test is +-0.5, so the total error on two tests can be up to 1.0 and still be normal. However, mustard algae in particular can have very low FC loss overnight, so a loss of 1.0 could be mustard algae. The only way to be really sure is to do the test again using the test that measures by 0.2.
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