The current disclosure relates to a feed solution for an electrochemical generator, the feed solution comprising at least one of a chlorite solution and/or a chlorate solution, wherein hardness-causing ion concentration in at least one of the chlorite solution and/or the chlorate solution is reduced to less than 1 part per million using at least one of an ion exchange method and/or a precipitation method. The current disclosure additionally relates to an electrochemical chlorine dioxide generator wherein the reactant feedstock is an electrolyte solution passed through an ion exchange column, the ion exchange column capable of substantially removing hardness-causing ions in the electrolyte solution. The current disclosure further relates to a method for assessing acceptable concentrations of hardness-causing impurities in an electrolyte solution. Additionally, the current disclosure relates to methods for reducing impurities in a sodium chlorite reactant feedstock.