EC stands for electrical conductivity and measures the ability to conduct electricity through water and measures in microsiemens per centimeter (uS/cm).
The EC of a solution increases as salt is added to the fluid; horticulture nutrients are composed of salts. A typical EC for cuttings or small plants is about .5-1.0 and at peak fruiting/flowering/maturation of plant should be around 1.5-2.0 depending on sensitivity of plant.
TDS stands for total dissolved solids or the amount of mobile charged ions in a body of water. TDS measures in parts per million (ppm) or mg/L. TDS looks for minerals, salts or metals dissolved in water. A typical TDS reading for small plants or cuttings is 200ppm-500ppm. At peak of flowering / fruiting / maturation plant levels should read 1200-1600ppm.
Of course each plant has its own ability to uptake nutrients, so monitoring leaf development is key to ensuring proper feeding. If your nutrient schedule is calling for an increase in feed strength but your plant looks burnt or over fertilized its time to flush and reduce your nutrient strength.
For more indoor,outdoor, and hydroponics information, please visit San Diego Hydroponics & Organics website.