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Thread: Mysterious Calcium Hardness

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    Mysterious Calcium Hardness

    For the last month or so, the CH in the pool has been measuring 400 ppm. Today it measured 450 ppm and I don't have a good explanation for where the additional CH came from. I was so surprised I checked a 25 ml sample and counted 10 ppm drops.

    No one has added anything with calcium to the pool, expect fill water which measures about 50 ppm. But if I've done the math right I'd have had to evaporate all the water in the pool except a few gallons and refilled with 50 ppm water.

    There was a fire in the everglades over the past month which dumped some ash on the deck and I assume in the pool, filtered by the screen cage.

    Other than that I can't guess where it came from. Any thoughts?
    17,250 gallon plaster pool & spa, IC40 SWCG, Cartridge Filter, CYA 70-80, Boric 50 ppm, Temp~84F, Naples, FL.

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    JoyfulNoise's Avatar
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    Re: Mysterious Calcium Hardness

    Let me ask you this - are you titrating to the first moment you see blue or until the blue stops changing color (becoming more intensely blue)? Many people make the mistake and stop the test at the first sight of blue; that's incorrect. You titrate the sample until the blue stops changing; usually the difference is about 2-3 drops of R-0012. If that is not the problem, then try this -

    Add 10 drops of R-0010 (assumes you're doing a 10mL water sample test) and then add about 5 drops of R-0012. Finally, add the R-0011L indicator dye and then titrate with the R-0012. Count up all of your R-0012 drops, even the 5 initial ones. That sometimes helps to give a more repeatable result. You can add as much as half of the number of R-0012 drops you expect to use before adding the dye; it helps to lock up some of the calcium and any trace metals that might be in the water sample so that the endpoint is easier to see.
    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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    Re: Mysterious Calcium Hardness

    Thanks for this input, I'll give it a try.

    In the meantime I ran over to the pool store and had them make the test with their bigger rig and magnetic stirrer. They came up with 405 ppm, nearer my earlier number.
    17,250 gallon plaster pool & spa, IC40 SWCG, Cartridge Filter, CYA 70-80, Boric 50 ppm, Temp~84F, Naples, FL.

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    Re: Mysterious Calcium Hardness

    I never consider the readings to be exact. I always take readings over time and look for an average.

    50 ppm is a little bit wide for range but not too concerning.

    There are several things that can affect the levels or readings.

    If the water sample is not exactly the same, that will throw off precision.

    If you had several inches of evaporation without refilling, that can raise your levels.

    If your plaster is new, it can add calcium.

    If you had scale and it dissolved, that will add calcium.
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    Mod Squad YippeeSkippy's Avatar
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    Re: Mysterious Calcium Hardness

    Keep in mind that as water evaporates it also leaves behind the calcium. So your calcium can raise over time. Do you have high calcium fill water?

    Yip
    Maddie :) 12K Fiberglass IG, Infinity 4000 automatic cover, SWCG, Hayward Sand Filter, Hayward 1.5 Pump, Doheny Discovery Robot, Savi Melody LED pool lights, outdoor speakers and other assorted doo-dads. Sundance Altamar Hot Tub.
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    Re: Mysterious Calcium Hardness

    Thanks for the last two posts. I'm losing about 1/4" per day and the town water has 50 PPM calcium hardness. So to get a 50 PPM increase, nearly all the pool water would have to evaporate and then refill with 50ppm to get a 50 ppm increase.

    The pool is new, and recently I've been lowering TA and had the PH down to 7.0-7.2 for a couple days. Still, in my 17250 gallon pool it takes 8 lbs. of calcium chloride to bring the level up 50 ppm.

    I'll keep an eye on this over time and also follow the detailed CH instructions more closely.
    17,250 gallon plaster pool & spa, IC40 SWCG, Cartridge Filter, CYA 70-80, Boric 50 ppm, Temp~84F, Naples, FL.

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    JoyfulNoise's Avatar
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    Re: Mysterious Calcium Hardness

    Quote Originally Posted by Naplespool View Post
    Thanks for the last two posts. I'm losing about 1/4" per day and the town water has 50 PPM calcium hardness. So to get a 50 PPM increase, nearly all the pool water would have to evaporate and then refill with 50ppm to get a 50 ppm increase.

    The pool is new, and recently I've been lowering TA and had the PH down to 7.0-7.2 for a couple days. Still, in my 17250 gallon pool it takes 8 lbs. of calcium chloride to bring the level up 50 ppm.

    I'll keep an eye on this over time and also follow the detailed CH instructions more closely.
    8 lbs of calcium could easily be removed from the surface of your pool with only a microscopic change in plaster thickness. Calcium carbonate has an average density of 75 lbs/cu. ft. A small pool surface is easily 900 sq. ft of surface area (yours would be significantly larger than that). So if you do the math you'd get a change in plaster thickness of about 0.0002" (0.2mils) per pound of calcium carbonate dissolved. So one can easily dissolve a little bit of their plaster and get a good deal of CH increase.
    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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