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Thread: Understanding Calcium Hardness CH

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    Join Date
    Sep 2014
    Winter Springs, FL

    Understanding Calcium Hardness CH

    What exactly is the significance of Calcium Hardness (CH)? I understand it can manifest itself in either leaching calcium from a plaster pool (which i have) or leaving calcium deposits, but i'm not sure what affects it. Every time I do the CH test, it is the same - 450 or 475. I've been living in this house for about 9 months, and the pool was completely re-surfaced about a year ago. I've had to add in plenty of water (due to evaporation, and lettings some out for tile repair) over the past 9 months. Yet the results of the test are always the same.

    Mostly, the number is not in the range that the "Pool Math" says it should be. Do I need to be concerned about it?

    Pool Info:
    Type: In-Ground, Plaster, @13500 Gallons
    Filter/Pump: Hayward Star-Clear Plus (C1200) Cartridge Filter, Hayward TriStar VSP
    Age: Built in the 80's, but completely renovated and re-surfaced in 2014
    Test Kit: Tests done using TF-100 test kit

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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Understanding Calcium Hardness CH

    The only way for the CH to go down is by removing water (not from evaporation) and adding water that has lower CH. In fact when the water evaporates it leaves the CH in the pool and then when you refill, you are adding more CH ... so usually the CH climbs due to evaporation unless you get a lot of rain and have to dump water which would lower the CH.

    You CH is not terribly high and if you keep your pH in line < 7.8 you should be fine.
    Jason, TFP Moderator
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  3. Back To Top    #3
    Divin Dave's Avatar
    Join Date
    Oct 2013
    Longview, Texas

    Re: Understanding Calcium Hardness CH

    calcium in important in a plaster pool. Several things could happen if the chemistry gets out of whack.

    If you have too much calcium in the water and your pH gets out of hand, the calcium can precipitate out of the water and attach itself to the plaster resulting in calcium scaling

    on the flip side, if your calcium is too low, the water will leach calcium out of the plaster resulting in weakening the plaster and possibly pitting it.

    your CH is not terrribly high, its easily manageable.

    In all cases, pH plays a large role in whether or not the CH precipitates or leaches from the plaster. You need to be very diligent with keeping your pH within range. When you do not keep your pH within recommended levels, is when you realize problems with CH.
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge. Experience- it's what's learned just after you needed it most !!

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