A method of monitoring and controlling hardness in an industrial water system is described and claimed. The method requires the use of a Compound that develops a separate detectable fluorescent signal in the presence of soluble hardness. A fluorometer is used to detect this separate detectable fluorescent signal of the Compound. The separate detectable fluorescent signal is used to ascertain the amount of soluble hardness present in the industrial water system. Another aspect of the instant claimed invention is the ability to determine whether the soluble hardness is calcium or magnesium based.