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Thread: Effect of Temperature on Calcium Hardness Reading

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    Effect of Temperature on Calcium Hardness Reading

    Hi all.

    I was doing some testing of my tap water tonight, and noticed some strange behavior. Here are my results (I was only testing CH - looking to get a new water softener):

    Test 1 - Cold Water (60 degrees) - 380 ppm
    Test 2 - Hot water (120 degrees) - 150 ppm
    Test 3 - Cold water heated in the microwave (130 degrees) - 160 ppm
    Test 4 - Cold water allowed to come to room temp (70 degrees) - 400 ppm

    What gives? I've checked Taylor, and here, and I'm not seeing any documented link between temperature and calcium hardness results. I initially thought maybe my water heater was somehow removing hardness from the water, but the microwave test disproved that. Is there some compensation factor that needs to be applied to the calcium hardness test based on water temperature? Thanks!

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    Re: Effect of Temperature on Calcium Hardness Reading

    I think it may be pH related, pH is temperature dependent.

    I did my own little experiment this morning, nothing scientific at all:

    25 mL sample at 14,4 °C has a pH of 9,1, when I added 20 drops of buffer pH then reads 12,5
    25 mL sample at 54,0 °C has a pH of 11, wnen I added 20 drops of buffer pH then reads 11

    The Standard Methods mention that for the EDTA calcium test the pH has to be raised high enough to precipitate magnesium, they say 12 to 13.

    But then again you couldn't be reading total hardness at that temperature, the difference you measured is just too important.

    So I don't know. Good question though!

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    Re: Effect of Temperature on Calcium Hardness Reading

    I can't answer the testing part of the question but I can tell you that calcium is more soluble in cold water than hot.

    Taylor has a good tech line at 1-800-TEST-KIT that I'm sure could answer the question fully.
    21' Leslies Beachland Ag Pool, 10,000 gallons, professionally installed (best money I ever spent) Hayward 16" sand filter w/Pentair two speed pump Fafco 4x20 solar heater,Aqua Trol RJ. Borates added. Hard plumbed.

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    Re: Effect of Temperature on Calcium Hardness Reading

    I E-mailed Taylor about this and they said that you should not be using the Calcium Hardness test (or any other test) above 100F. The tests are designed and calibrated for room temperature.

    Richard
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Effect of Temperature on Calcium Hardness Reading

    I believe JasonLion has said pH fluctuates with temperature so that test should be done at the sample's original temperature?
    BBB "Intermediate Swimmer"
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    JasonLion's Avatar
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    Re: Effect of Temperature on Calcium Hardness Reading

    The PH of pool water will change with temperature, but that isn't necessarily the reason you should do the water testing at room temperature. Various chemical reactions will behave differently at different temperatures. I am not sure exactly why the CH test behaves strangely at high temperatures, but PH shifts are only one of several possible causes.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Effect of Temperature on Calcium Hardness Reading

    With the amount of variation I'm seeing, I'm concerned that I may not be getting an accurate (or even close) reading unless I bring the water closer to a optimal temperature. Tonight when I get home I'll do some more testing. I'll test for everything, not just CH, at multiple temperatures.

    This makes me wonder if I can trust the results I get when testing hot tub water, or very cold water (like right now).

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    Re: Effect of Temperature on Calcium Hardness Reading

    Well, the lesson to be learned here is not to let your pool get to 160 degrees because your CH testing will be off!!

    Just kidding, Tom. But, I do think it's important that an accurate test of your pool water ought to be done in normal pool water temps. That may get a little frustrating as we all want to get an early jump in the Spring but I think that any pool water less than 70 degrees or so should be brought inside and warmed to 80 and then tested.
    Dave S. - Forum owner
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