Hanna Instruments PH Calibration Combo Pack 4.0, 7.0, 10.0 Ideal for testing pH balance of drinking water, pool, aquarium, RO system testing equipment for pools, hydroponics, food processing, home aquariums, industrial Each of our pH solutions are nontoxic in low quantities. Clean with soap and water if exposed to skin These are the highest quality pH test solutions you can buy on the market today pH measuring tool that you can use and get 100% precise and fast readings