The Milwaukee Instruments pH600 Economical Pocket Tester is a simple and easy tool designed for testing aquarium water. The tester has a 1 point manual calibration, 0.1 pH accuracy and a range of 0.0 to 14.0 pH. The pH pocket tester kit comes with calibration screwdriver, batteries and instructions. For first use, hold the sensor end in the calibration solution. For freshwater, use the 7.01 calibration solution. Acid water systems will use the 4.01 calibration solution and the saltwater aquariums will use the 10.01 calibration solution. Once done, use the screwdriver to change the pH to 7.0 and then check your water. Keep the meter wet and do not use RO or distilled water to calibrate your pH meter.