How important is the conductivity of the nutrient solution?

Conductivity measures the concentration of the nutrient solution and, therefore, must be adjusted to the needs of your plants. The higher the conductivity, the richer the solution is in nutrients. Put simply, if the conductivity is too low, this can lead to deficiencies, whereas, if the conductivity is too high, this can lead to toxicity.
Delicate plants, cuttings and seedlings need a low conductivity. Once the plants begin to grow, they need a more concentrated nutrient solution. Therefore, conductivity must be increased by adding nutrients. Some plants prefer less concentrated nutrients whereas others grow better with a higher concentration.