In basic terms, pH is an indication of the acidity or alkalinity of a fluid. Water has a pH of 7, which is neutral. An acidic fluid will range from 0-7 pH, and an alkaline fluid will have a range of 7-14 pH.
pH levels in your coolant drop due to bacterial emissions. Since coolants have an operating range of 8-10 pH, even a .2 drop in pH level can cause a host of problems, ranging from rusty machines and parts to sump odor and skin irritations. With consistent pH monitoring and bacterial control methods, these problems can be prevented.