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Thread: Overnight chlorine increase

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    Overnight chlorine increase

    I'd been a bit slack in my testing and apparantly let me chlorine get a bit low. The pool clouded up some, and I assume it was an algae infestation that couldn't take entire control. I My CYA is around 40, so I used a shock level of 16. I have been doing the overnight test for about one week now. 7/25 pm FC 14.5, CC .5, 7/26 pm FC 15.0, CC .5. I figured that this was just a testing error, since I was within .5. 7/28 pm FC 10.5, CC 1.0, 7/29 FC 12.5, CC .5! Now I suppose the most reasonable thought is I somehow screwed up in testing last night. But is it possible for the chlorine to increase 2 hours overnight?

    How long from additiion of cholrine should you test? Last night I added chlorine and then went out. When I got back about 2 1/2 hours later, the timer had shut off (forgot to tell LLP(lovely life partner)) to keep the pool running. I tested shortly after turning the pump back on. Could it be possible that the chlorine hadn't circulated enough and gave a false reading?

    Johanna
    1984 vintage 16x32 Doughboy vinyl AG w/deep end, Sand Filter

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    Re: Overnight chlorine increase

    Johanna,

    The overnight FC loss test should be done only after your water is clear. Is it?

    Secondly, you are either not doing it correctly or not reporting the numbers correctly. Reread in Pool School how to do the test.

    I think if you can post a full set of test results and the appearance of your water, we can be of more help.
    Dave S. - Forum owner
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    Re: Overnight chlorine increase

    If you have a SWG or tricglor tablet feeder, FC can increase overnight. Otherwise it is a testing error of some kind. You need to wait at least 30 minutes after a chemical addition, with the pump running, before testing. You also want the pump running for an hour before you take a sample to test with.
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    Re: Overnight chlorine increase

    Quote Originally Posted by duraleigh
    The overnight FC loss test should be done only after your water is clear.
    I thought one of the nice things about having a fas-dpd test was the ability to stop shocking (thereby saving money) before the pool is clear by being able to identify when the algae is all dead. I am basing this off a few things, including this article and thread:
    pool-school/shocking_your_pool
    how-to-shock-article-update-suggestion-t14672.html
    16x32 21,000 gallon in-ground exposed aggregate, 1.5hp pump, 120 sqft catridge filter, birdcage, solar panels, aquavac tigershark qc robot.

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    Re: Overnight chlorine increase

    Quote Originally Posted by reebok
    I thought one of the nice things about having a fas-dpd test was the ability to stop shocking (thereby saving money) before the pool is clear by being able to identify when the algae is all dead.
    That is what I believe, but not everyone agrees with me about it. Essentially, you can stop if you know what you are doing and are doing the test correctly, etc. But some people use that statement as a license to stop shocking after an OTO test still reads high the next morning, which doesn't work.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Overnight chlorine increase

    What I see on the forum frequently is,
    "My FC held overnite and my CC's are .5.....Why is my pool still cloudy"
    The answer invariably is that the tests were not performed properly. However, rather than review the techniques and how pertinent it is to do the overnite test with FAS/DPD only, I like to add the criteria of clear water as well.

    That pretty much eliminates the other errors that can and do happen to newbies and it is what they were all trying to accomplish anyway.

    The chlorine savings would generally be small (but notable) compared to being able to swim a little sooner or possibly even continuing to fight algae in a "break even" pattern for several more days.
    Dave S. - Forum owner
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    Re: Overnight chlorine increase

    I appreciate all of the replies. My water is clear. I've been using this method since last year, and think I know how to do the chlorine test. I am using bleach, so there is no additional chlorine added overnight. I just got home this evening and haven't done a full test tonight. But last time I tested anything other than PH and chlorine, my TA was 110 and CYA 40. My Ph has been about 7.5 (I never feel real comfortable with those color matching tests). Maybe I was just tired last night, it was pretty late when I was able to test the water!

    Johanna
    1984 vintage 16x32 Doughboy vinyl AG w/deep end, Sand Filter

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    Re: Overnight chlorine increase

    I have been doing the overnight test for about one week now. 7/25 pm FC 14.5, CC .5, 7/26 pm FC 15.0, CC .5. I figured that this was just a testing error, since I was within .5. 7/28 pm FC 10.5, CC 1.0, 7/29 FC 12.5, CC .5!
    I've been using this method since last year, and think I know how to do the chlorine test.
    The test I am referring to is the Overnite FC Loss Test.

    That test requires a result in the evening and then another test and result the next
    AM. The post for an Overnite FC Loss Test should look something like this example.

    7/26 -7:30PM FC-16.5 ......7/27 6:00AM -FC-16.0

    In your post, you only report PM testing and that's what is confusing me.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Overnight chlorine increase

    The drop sizes may have been different and would cause your test results to be slightly different.
    Buggs

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    Re: Overnight chlorine increase

    OOPS! That should have been -- 7/25 pm FC 14.5, CC .5, 7/26 AM FC 15.0, CC .5. and 7/28 pm FC 10.5, CC 1.0, 7/29 AM FC 12.5, CC .5!

    Clearly this is a testing error on my part because last night I tested the chlorine twice, withing about 15 minutes and came out FC 11.5, CC 1.0 and FC 12.5, CC 1.0. This morning it was FC 11.5, CC.5. I suppose I shall have to work at being more consistent with my drops! It was always my understanding that the bottles were designed so that the drops would be consistent.

    Johanna
    1984 vintage 16x32 Doughboy vinyl AG w/deep end, Sand Filter

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    Re: Overnight chlorine increase

    For uniform drop size, you want to hold the dropper bottle vertically, squeze gently so the drop falls off the tip when it gets heavy enough instead of "spraying" out, and wipe the dropper tip once in a while with a damp tissue.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Overnight chlorine increase

    Thanks for the tips on consistent drops! I will try that out tonight. The good thing is that my pool looks gorgeous again. so hopefully what I have been doing is working, even if my readings aren't! I will continue with the overnight drop test again tonight and see how I come out.

    Thanks again,

    Johanna
    1984 vintage 16x32 Doughboy vinyl AG w/deep end, Sand Filter

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