Testing for Chlorine vs Bromine

[The Mule]

Hi All! I've been lurking and reading a lot on this forum since early January when I got this spa, and really, really appreciate the wealth of knowledge here!

I'm using the 3-stage bromine process and an OTO-type test kit. It's my understanding that you can't easily distinguish between chlorine and bromine without a bromine specific kit like the Taylor 2106, and if you add the proper amount of sodium bromide (to get 30 ppm) at each tub fill-up, then there isn't any real need to test for it.
So my question is, when I add bleach, (say 1/4 cup of 8.25% bleach in 130 gal water) about how long does it take for the chlorine to dissipate so that only bromine is left, and what I see on the OTO test is actually bromine not chlorine?

 

[chem geek]

Welcome to TFP!

Actually the Taylor bromine test kit doesn't distinguish between chlorine and bromine. All of these kits can't tell the difference. The reason for separate kits is that you don't need to (nor are you able to) test for Combined Bromine and you don't need the Cyanuric Acid (CYA) test. The units of measurement for chlorine and bromine are different where 1 ppm chlorine is 2.25 ppm bromine.

The chlorine will react with the bromide turning it into bromine rather quickly in minutes. Whether it's still chlorine or it's become bromine, the measurement on the OTO and any other test will be the same except that a chlorine test will give you chlorine ppm units while a bromine test will give you bromine ppm units, though for some test kits that show both, they use a simplified factor of 2 so that 1 ppm chlorine is 2 ppm bromine, but that's just an approximation.

 

[The Mule]

Thank you very much!