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Thread: 3 or 7

  1. Back To Top    #1



    Join Date
    Jul 2012
    Location
    Whidbey Island, WA
    Posts
    392

    3 or 7

    If PoolMath says recommended FC range is 3 to 7

    is there any advantage to maintaining 7 over 3?

    Thank you
    IG under fir trees and one cherry surrounded by grass built in 1979, 30k, plaster, old Sta-Rite HRPB30, 4.9 sq.ft, 20 GPM/sq.ft., but with new glass, new (in 2012) 1 HP WhisperFlo one speed, new (in 2013) Rainbow tab chlorinator attached at the top, old Maxi-Flo Heat Exchanger MF-260, Burnham V7 oil heater 245 MBH, new (in 2012) Compool to Easytouch, Taylor K-2005 and TF-100.

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    Mod Squad JVTrain's Avatar
    Join Date
    Feb 2014
    Location
    Central Minnesota
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    5,079

    Re: 3 or 7

    3 must be maintained as a minimum, at all times. 7 is a recommended target where if you are manually chlorinating with bleach, you should add enough to get you to 7 ppm each day. Theoretically, it's the most cost efficient to maintain chlorine at a lower level as chlorine is lost as a percentage to sunlight each day. For example, say your pool loses 30% of its chlorine each day to sunlight only. If you start at 7 ppm, you'd lose 2.1 ppm, ending the day at 4.9. If you start at 5 ppm, you'd lose 1.5 ppm, ending at 3.5 ppm. You can see that over time, you're losing less chlorine each day and saving money targeting 5 ppm instead of 7 ppm. But the BIG caveat here is that at the end of the day, your FC cannot drop below 3. This is for illustration purposes only and of course, chlorine demand is not that simple but gives a general idea. This is why SWG pools can be maintained at a slightly lower FC for their CYA level because the FC is being added over a longer period of time with less spikes up and down of FC than manual chlorination. Liquid chlorine/bleach stenner pump systems are another way to moderate chlorine rise and fall throughout the day.

    All that being said, I'd rather "waste" a few FC and a few cents a day by making sure my FC is always above minimum. My minimum is 3 FC but most days it never goes below 4.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
    Isolated Spa - 345 Gallons

  3. Back To Top    #3



    Join Date
    Jul 2012
    Location
    Whidbey Island, WA
    Posts
    392

    Re: 3 or 7

    thank you, got it, helpful
    IG under fir trees and one cherry surrounded by grass built in 1979, 30k, plaster, old Sta-Rite HRPB30, 4.9 sq.ft, 20 GPM/sq.ft., but with new glass, new (in 2012) 1 HP WhisperFlo one speed, new (in 2013) Rainbow tab chlorinator attached at the top, old Maxi-Flo Heat Exchanger MF-260, Burnham V7 oil heater 245 MBH, new (in 2012) Compool to Easytouch, Taylor K-2005 and TF-100.

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