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Thread: FC Degradation Rate

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    Smile FC Degradation Rate

    Is the degradation of FC from sunlight (not algae or other organic material) linear or exponential with regard to the level of FC in the pool? In other words, all else being equal, does a level of 14 FC degrade faster than say a level of 8 FC? Are there any links or references that expands on this subject?
    38,000 gallon, plaster pool. 39 years old, once re-plastered.
    60 sf DE filter, 1 1/2 HP Whisper Flow pump, 400,000 BTU/hr heater.
    Kreepy Krauly self cleaning system.

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    Mod Squad tim5055's Avatar
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    Re: FC Degradation Rate

    It is exponential

    Here is quote from Richard (Chem Geek) :

    Quote Originally Posted by chem geek View Post
    The limiting half-life for HOCl/OCl- is 35 minutes which is consistent with pool studies, but some experimental studies give 11.6 minutes.
    You can read the entire post here: Pool Water Chemistry
    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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    Re: FC Degradation Rate

    Quote Originally Posted by tim5055 View Post
    It is exponential

    Here is quote from Richard (Chem Geek) :



    You can read the entire post here: Pool Water Chemistry
    Thank you. Can I then conclude that if hypothetically I needed on gallon of liquid chlorine per week to maintain a required FC level, that it would be better to add 1/2 gallon every 3 1/2 days rather than the full gallon once a week? Or is there something else I may be missing?
    38,000 gallon, plaster pool. 39 years old, once re-plastered.
    60 sf DE filter, 1 1/2 HP Whisper Flow pump, 400,000 BTU/hr heater.
    Kreepy Krauly self cleaning system.

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    Mod Squad tim5055's Avatar
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    Re: FC Degradation Rate

    Quote Originally Posted by radaklj View Post
    Thank you. Can I then conclude that if hypothetically I needed on gallon of liquid chlorine per week to maintain a required FC level, that it would be better to add 1/2 gallon every 3 1/2 days rather than the full gallon once a week? Or is there something else I may be missing?
    Correct,,but even better would be 1/7th gallon every day as long as your CYA is correct. Once you go above the recommended FC level as a ratio to CYA the "unprotected" FC is what has a half life of 35 minutes.
    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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    Re: FC Degradation Rate

    Excellent, Tim. Thank you very much. I suspected as much, but you have confirmed it for me. I will adjust my chlorine additions accordingly.
    38,000 gallon, plaster pool. 39 years old, once re-plastered.
    60 sf DE filter, 1 1/2 HP Whisper Flow pump, 400,000 BTU/hr heater.
    Kreepy Krauly self cleaning system.

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    Mod Squad tim5055's Avatar
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    Re: FC Degradation Rate

    Quote Originally Posted by radaklj View Post
    Excellent, Tim. Thank you very much. I suspected as much, but you have confirmed it for me. I will adjust my chlorine additions accordingly.
    This is why many of us automate chlorine delivery to the pool. Most common is the salt water chlorine generator, but many use liquidator or Stenner pumps.

    Here is my install- My Stenner Install - July 2014
    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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