It sounds like you're on top of monitoring your plant's nutrient levels. In this case, the discrepancy between your input (1.6 EC) and the runoff (2.2-2.4 EC) could indeed suggest a potential lockout.
Here's what might be happening:
Nutrient Lockout: The higher EC in the runoff could indicate that the plants are not taking up nutrients effectively. This could be due to a pH imbalance or issues with nutrient availability in the soil.
pH Levels: Check the pH of your soil. Nutrient uptake is influenced by pH, and if it's too high or too low, it can impact the plant's ability to absorb certain nutrients.
Nutrient Ratio: Ensure that the nutrient solution you're using has a balanced ratio of nitrogen, as well as other essential nutrients. Sometimes an imbalance can lead to nutrient lockout.
Flush the System: If you suspect a nutrient lockout, a flush with pH-balanced water can help reset the system. This involves watering with plain water until the runoff has a lower EC.
Monitor Soil Moisture: Ensure that the soil is not consistently too wet or too dry, as both extremes can affect nutrient uptake.
It's a bit of detective work, but checking pH levels and adjusting your nutrient solution accordingly could be a good first step. If the issue persists, a more thorough flush might be necessary. Keep an eye on your plants, and they should start responding positively with the right adjustments!