Patent ID: 6998057

Claim:
A method for controlling the level of free chlorine in an aqueous fluid comprising the steps of: a. providing a first aqueous fluid substantially free of free chlorine; b. providing water-soluble material, which is a source of free chlorine and chloride ion; c. admixing said first aqueous fluid with water-soluble material, thereby to produce a second aqueous fluid containing free chlorine and chloride ion; d. measuring the level of chloride ion in said second aqueous fluid by means of a chloride ion specific sensor; and e. controlling, if necessary, in response to the measurement of step (d) the level of free chlorine in said second aqueous fluid by the further steps of (i) adjusting the amount of first aqueous fluid admixed with the water-soluble material, (ii) diluting said second aqueous fluid with aqueous fluid substantially free of free chlorine, or (iii) a combination of steps (i) and (ii).