Hydroponic Essentials Essentials ESCAL87 8-Ounce Calibration Solution 7.0 Essentials ph buffer is a known solution of a certain ph value designed to test the accuracy of ph meters Also used to measure the ph of a nutrient solution Essentials buffer use two values of 4 and 7ph to calibrate ph testers Work in hydroponics i.e. 5.5-6.5 Available in 8-ounce