Deficiency

I'd wager if you looked at the labels, hopefully guarnateed analysis labels, you'd find plenty of calcium is provided. If not, it does look like a calcium deficiency. Look to have quite a few things added for ferts. This is more likely lockout than anything else. If yo know your mix is mild, maybe try a little more runoff when fertilizing. stick to a good wet-dry cycle. Other thing to check before fiddling with mixture is pH. Soil should be slightly acidic. Closer to ~7 will help with calcium uptake... if you are hanging out at 6 or below, this could also be a cause of what you see...