Effect of Chlorine Neutraliser on TA test?

[tomfrh]

Do chlorine neutralisers eg sodium thiosulfate (taylor R-007, CCL Alkalinity buffer) affect the TA test at all?, similar to how it can interfere with a Phenol red pH test? E.g. if you added too much (say 4 drops instead of 2) would it cause a wrong result?

 

[mgtfp]

I guess, this post answers your question:

Yes, at high FC the TA test goes from blue to yellow instead of from green to red. You can add more sodium thiosulfate drops (R-0007) to the initial water sample to neutralize the chlorine. If you can see the transition in color, the test is still valid.

The TA indicator dye is a mixture of bromocresol green that goes from blue to yellow and methyl red that goes from yellow to red. So when both dyes are active you go from blue+yellow=green to yellow+red=red. High FC levels react with the methyl red dye leaving only the bromocresol green dye that goes from blue to yellow.