A method of producing a biocide, comprising: providing a solution of a hypochlorite oxidant having a concentration from 4000 to 7000 ppm, wherein said hypochlorite oxidant is sodium hypochlorite; providing a solution of an ammonium salt having a concentration from 18 to 28%; diluting said solution of an ammonium salt with 10-50% of said solution of a hypochlorite oxidant to form an ammonium salt dilution; mixing a remainder of said solution of a hypochlorite oxidant with said ammonium salt dilution; wherein the amount of hypochlorite oxidant is equimolar to the amount of ammonium salt; wherein said mixing includes: monitoring a plurality of control parameters that indicate when a maximum yield of said biocide, which yield is attainable without degradation of said biocide, has been reached; wherein said control parameters are oxidation reduction potential, conductivity, induction and oxygen saturation; and wherein when said control parameter is ORP, conductivity or induction, then said yield has been reached when the value of said control parameter is at a minimum, and when said control parameter is oxygen saturation, then said yield has been reached when the value of said control parameter changes from a fixed value; and stopping the addition of hypochlorite oxidant when said yield has been reached; wherein said method comprises either: adding a plurality of discrete amounts of said solution of a hypochlorite oxidant to said ammonium salt dilution under mixing conditions; and measuring said control parameter after the addition of each discrete amount of said solution of a hypochlorite oxidant; or mixing a stream of a hypochlorite solution with a stream of said ammonium salt dilution in a mixing chamber at a starting ratio; holding the flow rate of one of said streams constant and gradually increasing or decreasing the flow rate of the other of said streams; and monitoring the value of said control parameter in a stream leaving said mixing chamber. providing a solution of a hypochlorite oxidant having a concentration from 4000 to 7000 ppm, wherein said hypochlorite oxidant is sodium hypochlorite; providing a solution of an ammonium salt having a concentration from 18 to 28%; diluting said solution of an ammonium salt with 10-50% of said solution of a hypochlorite oxidant to form an ammonium salt dilution; mixing a remainder of said solution of a hypochlorite oxidant with said ammonium salt dilution; wherein the amount of hypochlorite oxidant is equimolar to the amount of ammonium salt; wherein said mixing includes: monitoring a plurality of control parameters that indicate when a maximum yield of said biocide, which yield is attainable without degradation of said biocide, has been reached; wherein said control parameters are oxidation reduction potential, conductivity, induction and oxygen saturation; and wherein when said control parameter is ORP, conductivity or induction, then said yield has been reached when the value of said control parameter is at a minimum, and when said control parameter is oxygen saturation, then said yield has been reached when the value of said control parameter changes from a fixed value; and monitoring a plurality of control parameters that indicate when a maximum yield of said biocide, which yield is attainable without degradation of said biocide, has been reached; wherein said control parameters are oxidation reduction potential, conductivity, induction and oxygen saturation; and wherein when said control parameter is ORP, conductivity or induction, then said yield has been reached when the value of said control parameter is at a minimum, and when said control parameter is oxygen saturation, then said yield has been reached when the value of said control parameter changes from a fixed value; and stopping the addition of hypochlorite oxidant when said yield has been reached; wherein said method comprises either: adding a plurality of discrete amounts of said solution of a hypochlorite oxidant to said ammonium salt dilution under mixing conditions; and measuring said control parameter after the addition of each discrete amount of said solution of a hypochlorite oxidant; or mixing a stream of a hypochlorite solution with a stream of said ammonium salt dilution in a mixing chamber at a starting ratio; holding the flow rate of one of said streams constant and gradually increasing or decreasing the flow rate of the other of said streams; and monitoring the value of said control parameter in a stream leaving said mixing chamber. adding a plurality of discrete amounts of said solution of a hypochlorite oxidant to said ammonium salt dilution under mixing conditions; and measuring said control parameter after the addition of each discrete amount of said solution of a hypochlorite oxidant; or mixing a stream of a hypochlorite solution with a stream of said ammonium salt dilution in a mixing chamber at a starting ratio; holding the flow rate of one of said streams constant and gradually increasing or decreasing the flow rate of the other of said streams; and monitoring the value of said control parameter in a stream leaving said mixing chamber.