What's the purpose of Thiosulfate?

[BC]

Taylor's requires 2 drops pf R-0007 before adding R-0008. Just wondering why and if one didn't add it, what would be the result? Does it help isolate the base factor better (truer reading) by canceling out other factors that make up Total Alkalinity?
Thanks,
Barry

 

[JasonLion]

Thiosulfate eliminates any chlorine that might be in the water. This is done because chlorine can react with the dye causing the test to be more difficult to read correctly.

 

[BC]

Thanks,
Would not the amt thiosulfate required depend on how much chlorine is in the sample instead of the standard 2 drops?

 

[JasonLion]

Typically, the amount required is way less than 2 drops, fortunately adding extra doesn't cause any problems. Since it is tricky to know if you have added enough, the directions simply have you add way too much so you know it is taken care of.

 

[BC]

Cool. Thanks again, Jason - just what I was wondering about.

 

[Guest]

If the indicator dye turns blue instead of green (this occurs at high shock levels) then you can redo the test add an additional drop or two of thiosulfate when doing this test. If you don't your endpoint will turn light yellow instead of red. The test is still valid, just harder to determine the endpoint.

 

[BC]

Makes sense...never had that happen, but just curious about the reasoning. I never was one to blindly follow instructions without understandng the whys.
Barry