A turbidity probe works by sending a light beam into the water to be tested. This light will then be scattered by any suspended particles. A light detector is placed at (usually) a 90 degree angle to the light source, and detects the amount of light that is reflected back at it.

pH meter is an instrument used to measure acidity or alkalinity of a solution - also know as pH. pH is the unit of measure that describes the degree of acidity or alkalinity.