Problems with Micro-Nutrients
Zinc Deficiency
Problem: Younger leaves start yellowing in between the veins. Leaf tips get discolored and start dying. the leaves will take a unique banded appearance and the plant will stop growing vertically. There will be much less space between new nodes which will cause all the new leaves to start bunching together. If the plant is budding, it's flowers may start dying.
Solution: Flush your system with clean, pH'd water that contains about half the nutrients needed for the plant (including zinc, iron, and manganese). Watch to make sure that the problem starts to clear up on new growth within a couple of days.