Total chlorine

[rephil]

Re: Chlorine/CYA relationship

I realize this is an old thread, but it came closest to what I am searching for so I will resurrect. After reading chem geek's post about active vs. bound (to CYA) chlorine levels here, I was curious what our test kits are measuring. When I get a reading of 4...is that TOTAL (bound and unbound) or just the unbound/active level? Since I haven't come across any debate about this, I assume it is the total...but wanted to confirm since I did not know if the reagent would react to "bound" chlorine or not.

 

[JoyfulNoise]

The DPD-FAS test measures both free chlorine (FC) and then combined chlorine (CC). Free chlorine is made up of three components - hypochlorous acid (HOCl), hypochlorite anion (OCl-) and chlorine bound to CYA (HCy-Cl). HOCl/OCl- are considered active chlorine and the HCy-Cl is bound or reserve chlorine. So when you measure FC with your DPD-FAS test, you are measuring all of the active and reserve chlorine in the water.