by Jorge Cervantes
EC / PPM
Fertilizers (nutrients) carry an electrical current when dissolved in water. Nutrient (salt) concentrations are measured by their ability to conduct electricity through a nutrient solution. Add elemental salts / metals to a solution and electrical conductivity increases proportionately. Simple electronic meters measure this value and interpret it as total. Every salt in a multielement solution has a different conductivity factor.
Electrical conductivity (EC), conductivity factor (CF), and parts per million (ppm) are the scales used to measure overall fertilizer concentration. European, Australian, and New Zealand growers use EC. Some still use CF in parts of Australia and New Zealand.
Nutrient solutions used to grow marijuana generally range between 500 and 2000 ppm. A dissolved solids (DS) measurement indicates how many parts per million (ppm) of dissolved solids exist in a solution. A reading of 1800 ppm means there are 1800 parts of nutrient in one million parts solution, or 1800/1,000,000.
Let 10-20 percent of the nutrient solution drain from the growing medium after each irrigation cycle to help maintain EC stability. The runoff carries away any excess fertilizer salt buildup in the growing medium.