I always thought that since calcium is a semi mobile nutrient it shows up in the middle to top of your plant. Anyone correct me if I'm wrong. I see the brown spots on some of the newest growth, which to me is a Cal def. Some strains are CalMag whores especially at week 4-5. And if your running in something like pro-mix with a long veg time, you can deplete the ph buffering capabilities of the added lime. Ph can fluctuate sometimes locking other nutrients out as well. Just my 2 but I think without the light bleaching, it's most likely calcium.