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Thread: CH test turns purple?

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    CH test turns purple?

    If the CH test turns purple instead of blue is it the same thing? I ran the test twice and after 8 drops the sample turned a solid purple. On the second test I added 8 more drops and observed no change in the color - still same shade of purple. This past summer my fill water was 120-140 so
    I'm finding 80 to be surprising.
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    Richard320's Avatar
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    Re: CH test turns purple?

    No, not the same thing. From Extended Test Kit Directions:

    The sample may turn purple during the test, or go to blue for a moment and then turn back to red/pink. This is called a "fading endpoint" and is caused by interference from metal ions. If this happens, do the test again, but this time add five drops of R-0012 before adding any R-0010 or R-0011L. Remember to count the initial five drops in the total.
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    Re: CH test turns purple?

    Oh boy...metal ions? What am I looking for with those? Could the new liner have provided these?

    Thanks Richard!
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    Re: CH test turns purple?

    The fill water most likely did. The liner has no metal.

    Did the fill water from from a well or a municipal source? Wells are the #1 source of metals, usually iron in the water. Did you use any copper based algaecides?

    There are tests for iron and copper, the two largest culprits by far.

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    Re: CH test turns purple?

    We filled from the house/city supply. I didn't add any algaecide...but the installer might have as the fill finished when I wasn't home. I'll be talking with him today.
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    bobodaclown's Avatar
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    Re: CH test turns purple?

    how old are you chemicals?
    also here's the direct link to Taylor Technologies CH test issues:
    http://www.taylortechnologies.com/Chemi ... ntentID=70

    the problem your experiencing is towards the bottom of the page.

    Beware the Fading Endpoint

    Occasionally when testing calcium hardness you may get a purple endpoint instead of blue. This is called a "fading endpoint" and is due to interference from metal ions (most likely copper from algaecides, pipes, or source water). Retest, but prevent the interference by adding five or six drops of hardness reagent to the sample before adding the buffer and indicator. Then proceed as usual. Remember to count the drops of titrant added at the beginning when you calculate the total number of drops required to reach the endpoint.
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    Re: CH test turns purple?

    Thanks. The chems are about 13 months old...but there's no staining of the bottles and I've kept them in a cool dry place. If the floating end point variant of the test doesn't work then I'll replace the reagents unless I'm advised otherwise?
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    Re: CH test turns purple?

    13 Month old reagents can be the cause of false results...

    Curious, can poolrx, Nature2, or Frog mineral purifiers be a source of metal ions causing this as well?

    Chelating the water with 25oz @ 16kgal bottle of Natural Chemistry Metal Free or various others can only help.
    Be absolutely sure its a chelating agent, so many companies claim to remove metals when its only a sequesting agent.

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    Re: CH test turns purple?

    You know, I looked a the bottles more carefully on Sunday and the purple one is definitely stained. I'm ordering new ones today. I'm also going to go to my local mom and pop shop today or tomorow and have them run the test - they've been pretty consistent with my own testing in the past. I'll repost with results. I also need to test the fill water from the spigot to see if it turns purple too...
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    Re: CH test turns purple?

    Quote Originally Posted by ProPoolGuy
    Curious, can poolrx, Nature2, or Frog mineral purifiers be a source of metal ions causing this as well?
    I'm not using any of these.
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