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Thread: High Chlorine Loss but no CC

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    High Chlorine Loss but no CC

    It possible to be losing FC to organics even if testing is showing less than .5 CC. My CYA is 50-60 But I seem to be losing a lot of FC. I added bleach to get it up to 7, yesterday just before sundown. (although I didn't do a drop test to confirm after adding the bleach. I do know it jumped up to 5+ afterwards based on the basic test)

    Today at 5:30 pm it was down to 3.5 Does that sound reasonable due to sun alone? Should I be doing an overnight FC loss test even if I don't have an issue with CC?

    Thanks!
    16,500 gal, In-Ground
    Pebblesheen Prism Blue (replaster 3/2010)
    DE Filter
    1.5 HP Pentair Challenger
    TF-100 Test Kit

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    JasonLion's Avatar
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    May 2007
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    Re: High Chlorine Loss but no CC

    Yes, you can have algae or other organics and not have any CC.

    With CYA around 50 I would expect you to lose around half of your starting FC level over the course of a sunny day. That fits what you described very well.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: High Chlorine Loss but no CC

    So chlorine loss to sun is typically a percentage rather than an absolute number? If i bump my starting FC up to 8 or 9 I should still expect to lose half that? I was under the impression 2-3 ppm was more the norm....learning new stuff everyday on here.

    On a related note, what's the best way to keep the FC where it needs to be if you're away from the pool for a few days? I was using the pucks in a floater before swithcing to BBB so it wasn't an issue.
    16,500 gal, In-Ground
    Pebblesheen Prism Blue (replaster 3/2010)
    DE Filter
    1.5 HP Pentair Challenger
    TF-100 Test Kit

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    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,887

    Re: High Chlorine Loss but no CC

    If you don't have a SWG, then trichlor tablets in a floater is still a good idea when you are away.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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