In the CH test, is light purple same as blue?

[jamyers]

With the TF-100 kit's CH test, it says to count drops until the sample turns from red to blue. When I test for CH, the sample starts off pink, and goes to light purple at 36 drops, but it takes a total of 44-46 drops to get the purple to slowly change to an actual light blue. Same results with the FC varying from 5 to the current 16 shock, and pH from 7.6 to the current 7.2.

Which point should I use, the first color change or the actual blue? I'm thinking the first change, but ...

Today's test results:
CYA = 45-50
FC = 16
CC = 0
pH = 7.2
TA = 150
CH = 360 or 450, depending...

 

[linen]

It sounds like you have a fading endpoint. The extended test kit directions discusses what you need to do correct for this.

One other note...the ph test is not valid when the FC is above 10 ppm, ph reads high then.

 

[jamyers]

Thanks for the pointer, those extended kit directions are terrific, and sparked a lot of other good reading!

 

[ping]

Try adding the R-0012 first to the test before adding R-0010 or R-0011L. If your CH is 360 add 32 drops of R-0012 first, then 2 drops of R-0010 and then 5 drops of R-0011L. Make sure you are swirling the test while adding the drops. At this point go back to adding the R-0012 and continue swirling the test with each drop. The test should turn blue right away and avoid the purple color when finished with the test. You will need to count the original 32 drops and however many more of the R-0012 that it took to turn the test blue.

I have the same problem with the CH test that you are having and by only adding 5 drops of R-0012 isn't enough to help with the purple. What you really want to shoot for is adding about 90% of the R-0012 needed for the test before adding the other reagents. Hope this works for you and let us know. A speedstir helps with the accuracy and speed of this test.

 

[jamyers]

Thanks for the tips! I've got a speedstir, it's a wonderful gadget/tool.

Ok, after doing the fading endpoint, using 10ml instead of 25, mixing distiller water, and trying pings suggestion, heres what i found. The basic "fading endpoint" directions helped, but not enough for confidence. Both the "distilled water" and Ping's method yield the same results (CH = 525) consistently, so I'm confident with either method.

The high CH doesn't surprise me given my experiences with this pool over the last 5 yrs - scale on the edge tiles, white cloudy water when.using granulated chlorine, etc.

 

[jamyers]

THANKS for the help, you guys and this site are terrific!