EC stands for Electric Conductivity (mS/liter) and with that we measure the amount of (usable and unusable) salts in water or medium.
Plants that grow and flower rapidly must have sufficient nutrients available.
To measure the nutritional value (actually the nutritional salts) you use an EC meter. The EC meter simply measures the amount of electrical resistance in water and that also explains why a medium like soil must be wet if one measures it.
An EC meter measures a total sum of all salts.
An EC of 0.1/100L from one brand of fertilizer therefore does not have to have the same nutritional value as an EC of 0.1/100L of the other brand.
Many cheaper fertilizers contain many elements such as chloride, cadmium and other heavy metals. The EC meter also measures these elements.
Cultivators who grow their crop by weight also try to get the plant to absorb as many nutrient salts as possible for a heavier end result. These nutrient salts must be available and absorbable and preferably balanced in such a way that it stimulates each other to be absorbed by the plant.
The best way to measure this in nft systems is by withdrawing some water from the medium with a syringe and then measuring it.
In hydroponic gardening systems with a medium like for example Rockwool, it is the best to push the EC meter directly in the wet Rockwool to get the most accurate value.
For soil or coco peat, it is best to mix the mediums lightly with demi water in a cup and measure after soaking. It is not possible with normal water, because it count the EC levels of the water also.
Demi water you can buy at each gas station as water for batteries.
What EC levels for plants?
Unambiguous (target) values for the number of nutrient salts in a solution are difficult to give.
The EC depends, among other things, on the size of the plant, the type of plant, the amount of water, the number of times you drip, the lighting strength, the natural EC of your tap water, the temperature, and the humidity.
All this determines how much water and nutrition a plant needs.
The grower's preference also plays a role. There are growers who achieve excellent results with an 'irresponsibly' strong nutrient solution and others who also manage to reap an excellent harvest with a 'weak' solution.
In general it can be stated that a nutrient solution for a young plant have an EC value of 1.0 to 1.3 mS and that this may increase to 2.0 mS for an adult plant.
If the 'natural' EC of the tap water deviates much from the averages used by various brands of fertilizers (an average EC of 0.5 to 0.6 is assumed), then this difference in EC must be adjusted.
An example:
Grower A measures an EC of 0.5 in his tap water.
He wants to achieve an EC of 1.8 and therefore adds 1.3 EC of nutrients.
Grower B has harder water and measures an EC of 0.8 in his tap water. If he also wants to create an EC of 1.8, grower B only adds 1.0 EC of nutrients. That is 0.3 EC less than his fellow grower.
To provide as much nutrition as grower A, grower B must produce an EC value of 2.1.
You can also assume that the EC in the slab may be half a point higher than in the dripping water.
The level of the EC is also related to the number of drips.
A relatively high nutrient solution, as example with an EC of 2.7 spread over five drips of 500ml per plant, will cause fewer problems in the slab than a drip of 150 ml with the same solution, six times a day per plant.
In the latter case, the nutrient salts in the solution will evaporate, causing the EC in the slab to increase enormously. Those who prefer to drip more often should use a less strong nutrient solution.
In all cases, you need to know what the nutrient solution does in the medium. Therefore, depending on system, check the pH and EC of the drain water or directly in the medium every 2nd day.
Oxalic Acid
An EC meter also measures the amount of waste salts excreted by the roots. This oxalic acid is normally broken down in a well buffered soil, but must be pushed out of the medium in Rockwool mediums.
Recirculating drainage water back into the tank causes an increase in oxalic acid. Sometimes the EC level can even increase because of this. That is why you have to pump the entire system empty and replace the water at least once a week in DWC systems.
Oxalic acid can be a problem in coco peat. Coco peat can be distinguished in buffered and sterilized coco peat.
Buffered coco peat breaks down oxalic acid and only needs water and fertilizer when needed while sterilized coco needs water and fertilizer at least 6 times a day. Every watering in sterilized coco peat, there must be drainage to remove the built up oxalic acid from the pot.
