The electrical conductivity (EC) of nutrient solution to water is expressed as Siemens per cm (s/cm), millisimens for cm (ms/cm) or Microsimens for cm (µ S/cm). This measure can be made with an EC meter when you add fertilizer to increase the ion with electric charge.
EC is the measure of all ions that conduct electricity in the solution. The greater the amount of ions present in the nutrient solution, the more electricity there will be than conduct nutrient solution. (Increase in EC) Monitoring the EC value is crucial because if the solutions conductivity is too high we must reduce the amount of fertilizer used and vice versa.
To find out if you are using too much or too little fertilizer, monitor the EC value of the solution in the tank. Starting, for instance, with a concentration of 1.00 EC. The following day if the value is increased (eg 1.4 EC), it means that the plant absorbs less water then solution and it is too concentrated. We must therefore increase the amount of water. If the next day the EC value fell (for example 0.7 EC), the plant has absorbed the nutrients more quickly than water. We must therefore increase the amount of nutrients.
This shows that the plant itself tells you what it needs! There is no correct value of CIs to be respected but varies from garden to garden as each plant has different needs.
For convenience, EC measures are often converted into TDS by measuring instruments. TDS (total dissolved solids) is expressed in ppm (parts per million).
How to convert the value TDS (ppm) in EC (µ S / cm)?
Multiply EC (µ S / cm) x 1000 and divide 2 = TDS (ppm)
Ex. If your EC value is 1.2 µ S / cm
1.2 x 1000 / 2 = 600ppm
How do you convert the value EC (µ S / cm) in TDS (ppm)?
Multiply TDS (ppm) x 2 and divide 1000
Ex. If your value TDS is 700ppm
700 x 2 / 1000 = 1.4 µ S / cm
Reading Ec-conductivity ms / cm µ S / cm TDS
1 EC 1ms/cm 1000 µ S / cm 500 PPM