General Hydroponics? pH Test Kits make pH testing easy. Simply fill a test-tube halfway with nutrient, add a few drops of pH Test Indicator and observe the coloration of the liquid in the test vial. Many experienced growers prefer our pH Test Kit to expensive electronic meters because of its reliability and ease of use, which are important factors when the health of a valuable crop is at stake. Use 3 drops per 5 ml of solution.