General Hydroponics PH Test Drops makes testing pH 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 this pH Test Kit to expensive electronic meters because of its reliability and ease of use. Super concentrated, just a few drops per test. Measures from 4.0 to 8.5. Replacement solution (8 oz.) is available.