What is PPM/TDS?
TDS stands for Total Dissolved Solids and is measured in ppm or parts per million. One ppm is one part by weight of the mineral in one million parts of solution. In a laboratory, TDS is found by allowing the liquid to evaporate and weighing the particles left over. In hydroponics TDS is estimated using a converstion from the measure of electrical conductivity (EC). TDS is currently the standard of measurement that most US growers use. This will probably begin to change in the future as hydroponic manufacturers begin changing their products to EC.
