Apera Instruments PH60 Pocket pH Tester is designed for reliable and easy pH measurement for general water solutions, such as in hydroponics, horticulture, aquaculture, pools& spas, water treatment, cooling towers, environmental monitoring, beverage making, education, etc. The meter comes with a replaceable pH probe (PH60-E) for general water solutions pH test. The meter is also compatible with 3 other types of pH electrodes and an ORP probe (sold separately) for different applications such as solid samples and surface tests. NOTE: Add a few drops of 3M KCL liquid (included in the kit) to their test sample (usually low ion-strength liquid like distilled water or RO water), which will significantly help accelerate the stabilization without affecting the pH reading.