I am having a similar problem right now, unfortunately the pictures won't reveal much with this shitty camera. I too believe it is a calcium diff., but I am awaiting advice from others on the board. I also have slight curling of the leaves as you described on a few of the plants, if the nute burn isn't bad will it go away on its own? I only gave them 550 PPM and the plants are like in between 9-12 inches tall, I think they are plenty mature enough to handle that but I could be wrong.