Thanks Ben

that does help! So "shock" is a non technical non specific dose of oxidising agents, whereas "breakpoint chlorination" is used for a specific purpose ie inorganic chloramine destruction.

I will assume then that the numerous pool shock products have nothing to do with achieving breakpoint chlorination, but they are used as some sort of magic tonic?. Also, is it true to say that you would only use liquid chlorine to achieve breakpoint chlorination, and not other forms such as cal hypo etc?

Thanks