Quote Originally Posted by chem geek View Post
Maybe the stirring is causing the chlorine to outgas.
How, unless the pH is below 6.0?

I checked; the R0871 FAS solution shows a pH of 2.71. It's possible that when FC > 10 ppm (20 drops or 1.0 ml) that the acidity of the FAS overcomes the potassium phosphate buffer, and pushes the sample solution pH to 5.0 or below. If so, then Cl2 will be present in solution, and could be off-gassed under agitation.

I'll add a NEW test to the spread sheet, using 1 drop of R-0006 Base Demand Reagent, add to the water sample after adding DPD powder. I don't know if this will change the accuracy of the test, but it should reduce any off-gassing of Cl2.

http://www.taylortechnologies.com/MSDSS/0870.PDF
DPD powder => 60% potassium phosphate (pH ~7.2?)

http://www.taylortechnologies.com/MSDSS/0871.PDF
pH = 2.71

http://www.taylortechnologies.com/MSDSS/0006.PDF
Soda ash solution, pH => ~1.0