Quote Originally Posted by chem geek View Post
Thiosulfate is supposed to reduce chlorine directly and not form combined chlorines. There are many possible reactions, but one of them is the following:

Na2S2O3•5H2O --> 2Na+ + S2O3(2-) + 5H2O

2S2O3(2-) + HOCl --> S4O6(2-) + OH- + Cl-

There are other reactions that take the thiosulfate all the way to sulfate or even sulfur, but I believe these are less likely. None of them form combined chlorine -- all produce chloride ion. The oxidation potentials are as follows:

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Richard
Between your post and the chemical anlayis on this page, my eyes have gone buggy!

If Professional Pool Operators of America (PPOA) is correct, I would think that Sodium Sulfite is a better option than Sodium Thiosulfate beause there is no free Sulfur floating around "sulfinating" the water up.

I assume the Sodium sulfate (or Glauber's salt, sodium sulfate decahydrate, Na2SO4·10H2O per wikipedai) is just diluted into the water.

Anyway, I still don't know what my chlorine level is, but I'm trying to find a DPD test kit locally.