Consider this, the plant is showing some stress. Is that pot plastic, does it have good drainage, does it sit in run off is does it drain away. How often do you water, so you water till 10% run off or no run off. Soil looks dry. What ppm are you using. Do you ph after mixing, what is the ph going in compared to what is comming out. What is in your "soil", is it ammended? Be sure to use nutrients as instructed.
Do you have a picture of entire plant?