An EC meter measures 'Electrical Conductivity' otherwise simply referred to as 'Conductivity'. Conductivity is a measure of the amount of a small current that can pass through a given amount of liquid/solution. It is the dissolved salts - or nutrients - in the water which allow the electricity to flow. so when the concentration of nutrients is greater, more current will pass through the solution, when the concentration of the nutrients is lower, so is the current and thus the reading can be used as a measure of how strong or weak your nutrient solution is.
You can measure your nutrient solution to determine how strong or weak it is with an EC (electrical conductivity) or TDS (total dissolved solids) meter.
An EC meter usually shows the reading in either micromhs per centimeter (uMho/cm) or microsiemens per centimeter (uS/cm). 1.0 uMho/cm is equivalent to 1.0 uS/cm. A TDS meter usually shows the reading in milli- grams per liter(mg/l) or parts per million (ppm).
Measuring the conducitivty of your nutrient solution is, therefore, an important way of checking the strength of the total nutrient content in your feedwater to the plants. As there is no soil to hold on to nutrients for the plants, the nutrient levels in the water are critical, and a conducitivty meter gives an instant readout to let you know if everything is as it should be.
