Clean probes with dilute nitric acid (1% by weight), or a mild liquid detergent. Alternatively, you can use sulfuric acid or dilute hydrochloric acid. For more thorough cleaning, mix 50% isopropanol with concentrated hydrochloric acid. Rinse the probes well with distilled or deionized water and recalibrate the meter before use.
Unlike pH and ORP sensors, conductivity meters can be stored dry.