What does it do?
Nitrogen is a component of enzymes and is involved in all enzymatic reactions and therefore plays an active role in all metabolic functions.
What do you see?
Purpling stalks, yellowing leaves starting from the base of the plant. Leaves eventually fall away.
What can you do?
Raise the EC of your feed solution by increasing your base nutrients or by adding a nitrogen specific fertilizer, such as CoGr Buffer or Blood Meal.