pH meters are an electronic device which are used in hydroponics to measure the hydrogen ions in a solution. They test the acidity or alkalinity of your nutrient solution. As a general guide and with some exceptions, the optimal pH range of your nutrient solution should be between 5.5 and 6.0. Please see our Complete EC & pH levels chart for hydroponic plants for more information. We stock pH meters and pens from Bluelab, HM and Milwaukee.