A concentration monitor for monitoring a concentration of a plurality of use solutions, each of the plurality of use solutions being, at least, a concentrate in a diluent, each of the plurality of use solutions having a resistivity which varies as a function of both temperature and an amount of the concentrate contained in a given amount of the diluent. A resistivity probe is adapted for use with at least one of the plurality of use solutions for taking a measurement related to the resistivity of the at least one of the plurality of use solutions. A temperature sensor is adapted for use with the at least one of the plurality of use solutions for taking a measurement related to the temperature of the at least one of the plurality of use solutions. A controller calculates the concentration of the at least one of the plurality of the use solutions based upon a predetermined algorithm using the resistivity and the temperature for the particular one of the at least one of the plurality of use solutions, the algorithm being based upon knowledge of the at least one of the plurality of use solutions being measured.