EC meters and why we need them
Electrical conductivity (EC) plays a huge role in hydroponics. Basically, the higher the EC in your hydroponics system, the more the plant will hold onto the liquids and the slower they will evaporate from it. EC also indicates how many free ions you have in the water you use and thus - how many free electrodes will pass onto the plant. The electrical conductivity also influences the rate at which your fertilisers will get absorbed by the plants. An EC test will be needed before the actual start of your plant's growing and practically throughout the whole season.
What does an EC test prove and how does it help?
An EC meter does not only measure the conductivity of your hydroponic system, but also the amounts of fertilisers in it. The more fertilisers you put - the higher values the EC meter will show (usually). Although not all minerals would influence the plant, most will and because of this you need to keep a close eye on this factor. Conductivity needs to be as low as possible in the very beginning and then to be increased fast for the next growth stage,
TIP: Always use you understand and don't aim for the heavyweight ones if you're not clear enough about how they work. It could cost you your yields.