I’m surprised there’s so little discussion of the form of chlorine. Chlorine dissolved in water can be dissolved Cl2, HOCl, OCl-, and chlorinated cyanurates. T

I’m surprised there’s so little discussion of the form of chlorine. Chlorine dissolved in water can be dissolved Cl2, HOCl, OCl-, and chlorinated cyanurates. These are all in a pH-dependent equilibrium, and the latter is most of what you get when you mix “NaDCC” with water. HOCl is generally considered the best disinfectant, and OCl- is weaker. Chlorinated cyanurates are very weak (and fairly UV-stable and non-irritating) and can replenish HOCl and OCl- as they are consumed. Yet somehow the food-and-beverage-service standard for disinfection seems to be “100 ppm as Cl2” without regard to the balance of chlorine species. On the other hand, this paper tested concentrations up to 10000ppm, which is really quite high.