Re: What is electrical conductivity in hydroponics and how to measure it ?

Electical Conductivity (EC) is a fast, easy and cheap way to estimate the 
concentration of a hydroponic nutrient solution. An EC meter has two metal 
electrodes between which an electrical current flows in proportion to the 
concentration of ions in the solution. EC will be zero with distilled or 
deionized water. EC meters can automatically monitor the solution and inject 
ions if the solution EC decreases below a certain value or dilute it with water 
if the EC increases because the solution is getting too concentrated.  

You can estimate what the EC of a solution will be if you know the ion 
concentration in milliequivalents/liter. Milliequivalents/liter of all cations 
or all anions divided by ten approximates the EC in milliSiemens/cm. A 
milliequivalent is a millimole of charge. A millimole of a monovalent ion, such 
as potassium (K+) or nitrate (NO3-), is equal to one milliequivalent. A 
millimole of a divalent ion, such as calcium (Ca2+) or magnesium (Mg2+), equals 
two milliequivalents because there are two charges per ion.


References


Electrical Conductivity Basics


Story of Conductivity


pH and Conductivity