Combined Chlorine Testing Question

revitup

Active member
Nov 30, 2019
25
Pawleys Island, SC
I'm testing for CC using the Taylor K-2006C kit. When testing for CC I add the 5 drops of 0003 and the test sample turns a very very light pink. One drop of the 0871 turns it clear. I record that result as .5ppm CC. I sometimes will leave that test sample as is while I conduct other tests. It doesn't take long and that CC test sample turns pink again, a deeper pink than it turned when I originally added the 0003 for my CC test. What does that mean, if anything? Is my original .5ppm CC result still valid?
 

Donldson

TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
3,952
NW Ohio
Record the result when it changes to clear and you're done. That test will always return to pink when left sitting. And I mean always: one time someone who asked this question had spent over an hour adding more drops every few minutes to see if it would stop. It didn't.
 

JamesW

TFP Expert
Mar 2, 2011
16,599
Reagent R-0003 contains iodide, which reacts with combined chlorine and any other weak oxidants to form iodine, which then combines with the dpd reagents to create the red color.

Atmospheric oxygen can interfere with the test by oxidizing the iodide.

4I- + O2 + 4H+ --> 2I2 + 2H2O
 
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