Interpreting CH test color change

[kjbarth]

Have Taylor K-2006 test kit and I think I may be interpreting the color change for the CH test incorrectly.

For most of the tests in the kit, it's very easy to interpret the color change to get good results...
FC - pink to clear
TA - green to red
Salt - yellow to salmon redish

For me, the CH test color change is a little difficult to gauge or maybe I'm interpreting the color incorrectly. As I add R-0012 reagent, the color goes from red to purple at about 200ppm (20 drops) but I don't really get to blue though I keep adding the reagent, stopping at around 400ppm (40 drops). Should I be stopping the test when the color is purple or bluish purple OR do I continue testing until the color is literally blue??

 

[Bama Rambler]

You keep droping until the color doesn't change any more and then don't count that last drop. It really doesn't matter if it's not exactly blue.

 

[jp12]

The purple color means you have metal in the water ( I have the same problem ).

From the Taylor website: http://www.taylortechnologies.com/Chemi ... ntentID=70

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.