What does free chlorine mean in practice?
It mainly includes hypochlorous acid and hypochlorite ion, the proportion of which depends on the pH of the water.
When does it matter?
This is a fraction quickly available for disinfection; its absence does not mean the absence of chlorine bound in the form of chloramines.
Which solutions are related to it?
It is measured by the DPD test without delay, while simultaneously controlling the pH and the required level at the point of the process.