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Thread: Understanding CSI (Calcite Saturation Index)

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    steveg_nh's Avatar
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    Understanding CSI (Calcite Saturation Index)

    I'm helping a friend open up his pool and make sure his tests and water are in good shape. Things are looking very good, but CH is a bit high. But from what I remember last year (when we took this pool from green to clean), CSI must also be looked at before you determine if you really need to replace any water to lower it.

    First some background.

    24,000 gallon gunite pool, about 15 years old I'd say. Manually dosed (no SWG).

    Test Results:

    pH: 7.6
    TA: 90
    CYA: 0 (adding CYA to get to 40, so doing that way)
    FC: 5
    CC: 0
    CH: 475-500

    For his pool, we see CH as ideal around 300. But his CSI is 0.25. If I understand poolmath correctly, until you are below -0.6 or above 0.6, he is still ok and doesn't need to change out any water.

    If this is true, why not? What does CSI tell you, and why is it not an issue, even though it's way above the range?

    Thanks for the (upcoming) chemistry lesson!
    24'x40' 25k gal Imperial Mountain Pond IGP, full 28 mil VynAll Ocean Breakers liner. All Hayward system: 140k BTU HeatPro heat pump, 3/4HP single speed TriStar 2" Pump, DE6020 filter, AquaPlus Automation/Salt Chlorination, remote controls, ColorLogic 4.0 lighting. Polaris 280 w/PB4-60 BP. TF100 & K1766 test kits. Rinox Palazzo pavers and Spherik coping. Pool installed 9/2013, project completed 6/16/14.

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    JoyfulNoise's Avatar
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    Re: Understanding CSI (Calcite Saturation Index)

    Quote Originally Posted by steveg_nh View Post
    I'm helping a friend open up his pool and make sure his tests and water are in good shape. Things are looking very good, but CH is a bit high. But from what I remember last year (when we took this pool from green to clean), CSI must also be looked at before you determine if you really need to replace any water to lower it.

    First some background.

    24,000 gallon gunite pool, about 15 years old I'd say. Manually dosed (no SWG).

    Test Results:

    pH: 7.6
    TA: 90
    CYA: 0 (adding CYA to get to 40, so doing that way)
    FC: 5
    CC: 0
    CH: 475-500

    For his pool, we see CH as ideal around 300. But his CSI is 0.25. If I understand poolmath correctly, until you are below -0.6 or above 0.6, he is still ok and doesn't need to change out any water.

    If this is true, why not? What does CSI tell you, and why is it not an issue, even though it's way above the range?

    Thanks for the (upcoming) chemistry lesson!
    First off, you really want to stay within -0.3to +0.3. 0.6 is the outer limits of what's safe.

    Second, you can easily manage water with a CH of 500ppm. My water is 850ppm and I get no scaling. If you adjust (lower) your TA down to 60-80, you'll easily get close to 0 CSI. Also, you should use 40ppm as CYA since that affects CSI too. Test for salt at the pool store unless you have a kit for it, I bet your friends salt level is a lot more than 0. Salt also affects CSI.

    Finally, CSI tells you if scaling or etching of the plaster is possible. It does not predict how fast it will happen. If you can get your friends pool close to 0 CSI, it will be perfectly fine. No need to waste water.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Richard320's Avatar
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    Re: Understanding CSI (Calcite Saturation Index)

    Go plug all your numbers into poolmath and look at CSI. Then see what happens when the temperature goes up or down. See what happens when pH creeps up to 7.9. Heck, see what happens if someone slacks off and it gets to 8.

    +/- .6 it where it says it will start scaling or etching. In reality, the range is more like +/- .3 because there can be areas with poor circulation where the pH or the CH can be higher or lower.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    steveg_nh's Avatar
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    Re: Understanding CSI (Calcite Saturation Index)

    I did enter CYA of 40 in poolmath, just an FYI. But I did not adjust temp...I just adjusted temp to 60, and CSI is now 0.04. Perfect, right? And with these levels, at 82 degrees (summer temps), CSI would be 0.24. So as the water gets warmer, we should just lower TA....cool.
    24'x40' 25k gal Imperial Mountain Pond IGP, full 28 mil VynAll Ocean Breakers liner. All Hayward system: 140k BTU HeatPro heat pump, 3/4HP single speed TriStar 2" Pump, DE6020 filter, AquaPlus Automation/Salt Chlorination, remote controls, ColorLogic 4.0 lighting. Polaris 280 w/PB4-60 BP. TF100 & K1766 test kits. Rinox Palazzo pavers and Spherik coping. Pool installed 9/2013, project completed 6/16/14.

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    JoyfulNoise's Avatar
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    Re: Understanding CSI (Calcite Saturation Index)

    Quote Originally Posted by steveg_nh View Post
    I did enter CYA of 40 in poolmath, just an FYI. But I did not adjust temp...I just adjusted temp to 60, and CSI is now 0.04. Perfect, right? And with these levels, at 82 degrees (summer temps), CSI would be 0.24. So as the water gets warmer, we should just lower TA....cool.
    Pool Math assumes a small amount of salt if you put 0 in for salt. However, most people using chlorinating liquids, powders and muriatic acid will have chloride concentrations in the 1000ppm range if they are not doing fresh water exchanges. Salt modifies the CSI by a little bit so at some point you might want to get a reading on his salt (chloride level) to be more accurate.

    Yes, adjusting pH and TA targets will have very significant impact on the CSI value.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    steveg_nh's Avatar
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    Re: Understanding CSI (Calcite Saturation Index)

    Cool. Thanks.

    I can test his pool for salt, as I have the K1766 kit. So anyway, looks like all is perfectly fine with those CH readings. Thought so, and really cool to understand the relationships of all the various levels.
    24'x40' 25k gal Imperial Mountain Pond IGP, full 28 mil VynAll Ocean Breakers liner. All Hayward system: 140k BTU HeatPro heat pump, 3/4HP single speed TriStar 2" Pump, DE6020 filter, AquaPlus Automation/Salt Chlorination, remote controls, ColorLogic 4.0 lighting. Polaris 280 w/PB4-60 BP. TF100 & K1766 test kits. Rinox Palazzo pavers and Spherik coping. Pool installed 9/2013, project completed 6/16/14.

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