The main uses of EC in hydroponics
Nutrient solutions are generally made up by
following label dose rates. However, label dose rates usually fail to take
into consideration issues that could cause the nutrient solution’s
concentration to be either too high, or too low. This is where an EC meter
can be a useful dosing tool:
1. Setting the
target EC: When making nutrient solutions, EC
meters are useful for setting the target EC. The EC requirement depends on
factors such as the stage of plant growth and the type of medium. Burning
of roots or foliage can occur if the EC is too high. If the EC is too low,
deficiency symptoms can occur.
Refer to Table 11.30 for commonly recommended
EC levels for the main stages of growth. There is no need to be precise
with EC levels because plants will generally only consume what they need.
Most plant species will tolerate being above or below the recommended
value by at least 10%.
The target EC values in Table 11.30 do not
include the EC of the make-up water. The EC of the water must be added to
the target value. For example, if the recommended target EC is 2.0mS/cm
and the water has an EC of 0.3mS/cm, the EC should be set to 2.3mS/cm
(i.e. 2.0mS/cm + 0.3mS/cm). For further information on this concept see “Concentration
2. Maintaining the
target EC in recirculating systems: EC meters are useful
for monitoring and maintaining the EC as nutrient and water are consumed.
If the EC is too low, concentrated nutrient will need to be added to
prevent the risk of the solution becoming depleted in any one nutrient
Be aware that the EC reading is a “gross”
figure. It will not warn of an imbalance of nutrient salts, or the
accumulation of toxic or nuisance salts (e.g. sodium chloride) which are
often present in the top-up water. Therefore, as a precaution, the
recirculating nutrient must be frequently discarded
Performing EC readings and adjusting the EC of the nutrient solution
Check the meter’s calibration using a reputable
Stir the nutrient reservoir thoroughly before sampling. Ensure the
sampling container is clean by rinsing a few times with the nutrient
For recirculating systems, it is easier to
interpret EC readings by always ensuring the reservoir is filled to the
same volume before taking the sample i.e. if the reservoir level has
dropped to half, then the EC reading will be twice as high as what it
would be when full (assuming the top-up water contains nil salts).
Rinse the electrode in distilled water then remove any excess water by
either gently shaking, or wiping with a tissue. Immerse the electrode in
the sample and wait a few minutes** before switching the meter on and
recording the EC (Fig 11.3).
** Wait longer if the sample’s temperature is
significantly different from ambient.
Adjusting the conductivity:
a) If the EC is below target: Add nutrient
until the target is reached (do not use additives for this purpose). To
calculate this volume mathematically, refer to
b) If the EC is well above target: Add more
water (“top-up” water). To calculate this volume mathematically, refer to
When finished, rinse the electrode with distilled water. Store the
electrode in distilled water when not in use.
For converting EC values to "ppm" for Hanna, Truncheon or Eutech TDS