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Thread: Need advice for calcium hardness testing

  1. Back To Top    #1

    Join Date
    Jun 2014
    Location
    Bridgewater, NJ
    Posts
    31

    Need advice for calcium hardness testing

    Hi, I have done several tests on my pool for calcium hardness but I am having trouble pinpointing the level. I use a Taylor test kit.
    The first few times, after adding the calcium hardness liquid, I would get more of a magenta color than a true red. Adding the hardness reagent would turn the solution to a bluish-purple instead of a definitive blue. There would be a range of a several drops to get from where it looked plain purple to start getting a bluish hue.

    Finally, I noticed something in the instructions about metal ion interference and that adding some hardness reagent before would bind those ions. I tried this by adding 6 drops of hardness reagent to the 25 ml sample but still got the magenta and bluish purple. However, after getting to 24 drops and not seeing anymore change after swirling, I set it down and to do something else and came back in 2 or 3 minutes. The solution was now totally blue.

    The instructions don't say anything about a very slow color change. How fast is it supposed to happen? Should one drop take it from red to blue? Or is it supposed to be a gradual color change with several drops needed after going from red/magenta to a definite blue?

    This is a 6 year old pool but I am the new owner since December so I don't know what has been put in it.

    During these tests the other levels were as follows:
    FC 1 - 5 ppm
    pH 7.5 - 7.7
    TA 140 - 150 ppm
    CYA 42 - 46
    Irregular shaped vinyl pool - about 22K
    Hayward DE 6020 filter, Hayward Tri-Chlor Feeder
    Aqua Comfort Heat Pump Heater
    Polaris 380
    Taylor K-2006; FAS/DPD kit

  2. Back To Top    #2

    Join Date
    May 2014
    Location
    Current: Singapore Previous: Clayton, Victoria, Australia
    Posts
    584

    Re: Need advice for calcium hardness testing

    Welcome to TFP!

    CH test turning purple sounds like a fading endpoint.

    The extended test kit directions indicate that you should try a diluted test (see 4th bullet point in "notes").

  3. Back To Top    #3

    Join Date
    Jun 2014
    Location
    Bridgewater, NJ
    Posts
    31

    Re: Need advice for calcium hardness testing

    Thanks, Abigail. I didn't know about this thread.
    Irregular shaped vinyl pool - about 22K
    Hayward DE 6020 filter, Hayward Tri-Chlor Feeder
    Aqua Comfort Heat Pump Heater
    Polaris 380
    Taylor K-2006; FAS/DPD kit

  4. Back To Top    #4

    Join Date
    Jun 2014
    Location
    Bridgewater, NJ
    Posts
    31

    Re: Need advice for calcium hardness testing

    That did the trick! I had used the hardness reagent pre-treatment before with a 25 ml sample and the color change was very gradual and hard to pinpoint but with the 10 ml sample it came quickly at the 7th drop for a 175 ppm level. Since each drop represents 25 ppm, this is not as accurate but I interpret this to be the upper limit of the actual level. If I need to be more accurate (which I don't believe I do), I can not use the 25 ml sample and know that I should reach the endpoint with no more than 18 drops.

    I would have tried the diluted test but I did not have any distilled water handy.
    Irregular shaped vinyl pool - about 22K
    Hayward DE 6020 filter, Hayward Tri-Chlor Feeder
    Aqua Comfort Heat Pump Heater
    Polaris 380
    Taylor K-2006; FAS/DPD kit

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