Leaves turning yellow and dying

Looks like Cal def and maybe N unless the Cal def is so advanced thats the cause of yellowing (I have never seen that, doesnt mean thats not the case though), thats about all the info your gonna get, you haven't provided any useful info beside pics, the more info you give the better the answer you can get, that being said looks like overall deficiency either from lack of nutrients, ph, or some kind of lockout. What are you growing in, what are your in/out ph/ec readings, what, how often and how much are you feeding, and environmentals. If you provide that info its easier to diagnose and the answers are more likely to be correct. Its amazing to me that we dont have a standard form for info like that by default when you submit a question, guess we'll have to wait for GD 3.0 for that, hopefully GD 2.0 actually works by the time 3.0 comes out.