Calcium Hardness test turning purple before blue?

[ennoble]

I can't seem to get my calcium hardness test to go from red to blue, it always goes to purple and then blue even after trying the buffering approach (adding 5 drops of the buffering solution R-0012 before adding R-0010 & 11). When should i stop adding R-0012 -- at the purple change or actually when it turns blue? The difference is about 250 if i count at purple and 350 when i actually see blue. I guess both are OK assuming somewhere in there is right?

 

[PoolBrews]

When it actually turns blue. Red and blue make purple... so you start with red, and as you add solution that is meant to turn it blue, you will get purple for a short time in between until there is enough solution to turn it blue. Make sense?

 

[ennoble]

Thanks, makes sense.

 

[Dirk]

When I test my CH, I get purple, too, for some number of drops before it finally turns blue. When it turns purple, I slow down the titration. I might wait 5-10 seconds between drops, to allow the color to fully form. This MO usually reduces the count by a drop or two, versus going too fast and overshooting when the blue would have first formed.