do you have any details?
PH of water fed to plants, PH of run off. What you are using to feed, and the N-P-K ratio. How much you fed, how much you water, how often you water, the kind of soil mix you are using and if possible what the soil is comprised of. The EC of the nutrient solution and the EC of the base water you used would help a lot too! Temps, humidity, are circulation are all important things we need to know as well. At first glance i think light stress, but i cannot be sure with out ANY info about the grow.