HELP Leave problem that i cannot solve

Hello this is my first post and grow. I currently have six plants 4 of which are in rock wool mini cubes. I have encountered a problem i cannot diagnose. Ive searched all over forums and i even have 3 grow books from the bookstore. I have the marijuana garden saver which has so far solved all my problems. But i have encountered one that i can not solve. I have had the plants for about 3 weeks now. They have grown aprrox ten inches and i have one little guy whos stem broke and he has been stunted but he is on the up and upp. I included a few pics of my gardenbut really what the hell is wrong with my damn leaves????????? I was watering them once a day for 15 mins. Going light on the nutes balancing ph and using drip clean.

whats your temp? humidity? what kind of nutes? ph of the dirt itself after watering ( i.e runoff water works )

need more info. are the photos from the plants in rockwool? you should probably take a peep at the roots to see if they look healthy. if it's in a pot filled with rockwool cubes, 15 min a day probably has then completely saturated. it's hard to imagine that plants that size would drink enough to water that much.

I get that on 1 or 2 of my plants here and there out of the group. I have noticed that usually means I am lacking Calcium.