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Thread: Discrepancies in Levels for SWG Free Chlorine Numbers

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    john.esher's Avatar
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    Discrepancies in Levels for SWG Free Chlorine Numbers

    Today I entered a few days worth of data into Jesse's Graphical Pool Testing Log. It was there that I noticed the target FC level of 10
    for my CYA of 70. I thought according to the CYA/Free Chlorine chart, I should be targeting about 6.

    I'm trying to figure it as I approach the target so I can turn the SWG back on. I will give another day to drop if I should be at 6, or turn it on tomorrow morning of I should be at 10.

    My numbers:

    August 13, 2015 @ 20:40

    Temperature: 74
    pH: 7.4
    Free Chlorine: 11.5
    Combined Chlorine: 0
    Cyanuric Acid: *
    Total Alkalinity: 100
    Calcium Hardness: **
    Sodium Chloride: 2600

    *The last reading for CYA was 70, taken 8/6 before I ran out of reagent. More on order.

    **The last reading for CH was 110, taken 8/11 - not monitored all the time due to the AG vinyl.


    Intex 18' x 52" AG with Sand Filter Pump & SWG (Model ECO15110) about 7,600 gallons tested with a K-2006-SALT.

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    Mod Squad JVTrain's Avatar
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    Go directly to the CYA/Chlorine chart in my signature. For a SWG pool with 70 ppm CYA, the FC minimum is 3, target is 5. I'd keep it at 4-5.
    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
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    JesseWV's Avatar
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    The suggested FC levels in my Graphical Testing log are based on those found in PoolMath. It seems there's a slight discrepancy between PoolMath and the CYA/Chlorine chart.

    I wonder if PoolMath and my spreadsheet should be adjusted to more closely follow the chart?
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

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    Mod Squad jblizzle's Avatar
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    PoolMath should match the Pool School chart.

    PoolMath just shows the minimum for a SWG pool ... that is all that really matters anyway.
    Jason, TFP Moderator
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    JesseWV's Avatar
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    I was more concerned about the "Target" goal which is showing as 10 FC for 70 CYA, when the chart is only showing 5.
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

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    Mod Squad jblizzle's Avatar
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    Again ... the only thing that matters is staying above the minimum. Every pool will have a different target as their daily consumption will be different
    Jason, TFP Moderator
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    The high end of the range is not a Target so does not match the Pool School target column. It shows 10 for 70 ppm CYA regardless of SWG or using Bleach. I'm not sure how the high end of the range was calculated since it does not appear to be a fixed percentage, but it's higher than the Target in Pool School and the Target is not very meaningful anyway. One simply has to always stay at or above the minimum so one's own target for their pool is whatever it takes so that they don't go below the minimum before their next dose of chlorine.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    ChemGeek - That last sentence is very interesting. I've been wondering about that. Thanks for the clarity. Too many times I see folks get too caught up in the numbers and formulas and charts and ...
    This is supposed to be troublefree. All the resources are there to guide us towards understanding our pools. But they are really just guides. The pool is the final judge. Give it want it wants and it will be great.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Discrepancies in Levels for SWG Free Chlorine Numbers

    Quote Originally Posted by chem geek View Post
    One simply has to always stay at or above the minimum so one's own target for their pool is whatever it takes so that they don't go below the minimum before their next dose of chlorine.
    Just what I'm looking for. As it drifts into range, I'll be monitoring and adjusting SWG run time during the day.


    Intex 18' x 52" AG with Sand Filter Pump & SWG (Model ECO15110) about 7,600 gallons tested with a K-2006-SALT.

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