Managing EC Using Run-off

Managing EC or (Electrical Conductivity) in your nutrient solution is essential for maximizing the growth rate and yield of your cannabis plants. You can learn more about the importance of EC and how to set the right targets in our tutorials “Cannabis Feeding Fundamentals” and “Understanding Electrical Conductivity (EC) and Osmosis.” To find the perfect EC levels for your fertigation, check out our tutorial “Setting EC Targets.”

It’s worth mentioning that the EC of the nutrient solution in the root zone often surpasses the inflow EC due to a gradual increase as the solution sits in the pots. The management of feeding frequency plays a crucial role in regulating the root zone EC. Longer intervals between feedings can result in more significant disparities between the inflow EC and the root zone EC.

While directly measuring the EC of the nutrient solution in the root zone isn’t practical, we can rely on the run-off produced during feeding as an indicator of the nutrients available to the plants. Measuring the EC of the run-off serves as a proxy for estimating the root zone EC.

In our tutorial, you’ll find extensive advice on how to handle the run-off EC effectively. We discuss the ideal range for your plants and provide strategies for addressing various EC situations. For a deeper insight into the significance of EC, we encourage you to explore our article titled “Understanding Electrical Conductivity (EC) and Osmosis.”

Measure the EC of the Run-off

Measuring the Electrical Conductivity (EC) of the run-off is a straightforward process, and you can do it inexpensively with meters available for as little as $15-$20. Personally, I rely on a Truncheon Pole, which I’ve confirmed to be accurate when compared to other meters. These meters use straightforward technology, so there’s no requirement to invest in a costly EC meter. Just immerse it in either the nutrient solution you’re feeding to the plant or the run-off flowing through the medium, and it will activate and promptly show the EC of the solution.

It’s of utmost importance to maintain a consistent schedule of measuring both the inflow and periodically the run-off EC. In the beginning, it’s advisable to check the run-off daily until you become familiar with the patterns and trends. Once you have a good grasp of the situation, you can skip some days, but it’s essential to never go more than a few days without checking the run-off EC for each plant.

For precise run-off EC measurements, it’s best to test the water right as it exits the pot, before it can mix with dissolved salts in the saucer. Personally, I find it convenient to use a large oral syringe to collect samples from the saucers of each plant. I then transfer this water to a small cup and submerge the EC meter to obtain a reading. Don’t forget to document these readings in your grow journal to monitor the EC performance of each plant over time.

Run-Off: EC Targets and Corrective Actions

Run-off EC Should be within 300 Points of Inflow EC:

Keeping the run-off EC at the right level is essential for ensuring optimal plant growth. Ideally, the run-off EC should generally stay within 300 points of the inflow EC, with a slight increase being acceptable. However, if the run-off EC exceeds +400, it’s time to take corrective measures.

If Run-off EC is High:

When you encounter a high run-off EC, the most efficient remedy is to increase the frequency of feeding. This step helps prevent excessive evaporation losses between fertigation events, which can lead to an increase in EC. If increasing the frequency isn’t enough to resolve the problem, you can also augment the amount of nutrient solution administered during each fertigation. This ensures thorough saturation of the growing medium and aids in lowering the salt concentration in the root zone. As the EC returns to the acceptable range, you can gradually reduce the quantities used.

Flushing with a lower EC solution should only be considered if the run-off EC is persistently high and poses a risk to the plants.

If increasing frequency is not practical or not helping, then you should increase quantity of nutrient solution applied at each feeding to to make sure you are getting a thorough saturation of the media. Increasing the quantity of run-off should help lower the quantity of salts in the root zone by flushing the access off in the runoff. Quantities may be reduced as EC returns to the acceptable range.

Only if run-off EC is dangerously or persistently high, should flushing with a lower EC solution be considered.

If Run-off EC is Low:

Conversely, when you consistently observe a low run-off EC, it’s less common but can occur temporarily. In most instances, this corrects itself within approximately four fertigation events. However, if the problem persists, it may signal an issue with insufficient water distribution during fertigation, particularly in automatic watering systems. Inadequate distribution can result in salt buildup and potential plant damage, even when the run-off EC remains low. In such situations, it becomes crucial to ensure proper water distribution within the growing system.

Remember to refer to our “Maintaining a Hydroponic Reservoir, for detailed information on managing water distribution in automatic watering systems to prevent EC imbalances.

EC Run-off Guidelines:

To manage an increasing run-off EC effectively, the most practical approach is to enhance the frequency of fertigation. If that’s not feasible, the next option is to increase the volume of run-off during each event. These measures typically prove effective in keeping the run-off EC within the acceptable range.

Nevertheless, if these methods prove insufficient in regulating the run-off EC, the next step is to contemplate reducing the EC of the inflow. This can be achieved through a process known as “Flushing to Lower EC.” Our tutorial, titled “Maintaining a Hydroponic Reservoir,” provides comprehensive guidance on when and how to perform this flushing procedure.

It’s essential to emphasize that flushing should only be considered as a last resort after exhausting other methods and when the run-off EC remains unmanageable. Proper monitoring and adjustment of fertigation frequency and run-off volume are the preferred approaches for maintaining the desired EC levels.

Guidelines for EC Run-off:

If Run-off EC is: (Compared to inflow)	Status	Action
Lower than inflow EC	Anomaly	Not a problem. Should self-correct.
Within +200*	Ideal	Monitor EC twice weekly
+200 to +300	Acceptable	Monitor EC daily, consider increasing feeding frequency to help flush out built-up salts.
+300 to +400	Caution	Increase Feeding frequency and/or Increase quantity of run-off to help flush out built-up salts.
+400 or Higher	Danger	Consider flushing: See “Pre-Harvest Flushing”

*EC values expressed in Microsiemens. 200 microsiemens = 0.2 millisiemens

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