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Thread: FC and sunlight - Overnight FC drop

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    TimS's Avatar
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    FC and sunlight - Overnight FC drop

    I've seen a number of posts regarding the effects of sunlight on FC and performing an overnight FC drop test. My pool is on the east side of the house, so with the exception of a couple of days in June, the pool is not exposed to direct sunlight after about 7:00pm, and is fully shaded as early as 6:00pm by the end of September. In addition, there are quite a few trees to the east of the pool, so I don't get direct sunlight on the pool until about an hour after sunrise.

    So, my questions:
    1. Does indirect sunlight have a noticeable impact on FC?
    2. When doing an overnight FC drop test, do you need to wait until dark to test, or only until there is no direct sunlight on the pool?
    3. When testing again in the morning, do you need to again test before sunrise, or only before the pool is exposed to direct sunlight?
    4. Is there some maximum number of hours to wait between tests? For example at least 6 hours but not more than 9 hours?

    TIA
    24' AG Round (vinyl replaced 0909) - 13500 gal - Sand Dollar Filter (150lb) - Dynamo DYNII-N1-1 1HP - Hayward HP380 Heat Pump - TF-100.
    Central Missouri

    Before I speak, I have something important to say.

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    duraleigh's Avatar
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    Re: FC and sunlight - Overnight FC drop

    Any testing improves in accuracy as you reduce the variables. Indirect UV has some effect, so if I needed a truly accurate result, I would eliminate the indirect UV from the test.

    Same with length of time between tests.....a longer testing period will result in greater accuracy so, when, practical, it makes sense to use the longest exposure time possible........but without the indirect UV.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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  3. Back To Top    #3
    TimS's Avatar
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    Re: FC and sunlight - Overnight FC drop

    OK, thanks for the clarification.
    24' AG Round (vinyl replaced 0909) - 13500 gal - Sand Dollar Filter (150lb) - Dynamo DYNII-N1-1 1HP - Hayward HP380 Heat Pump - TF-100.
    Central Missouri

    Before I speak, I have something important to say.

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