he's locked out on the mag side. If it were calcium it would show more round spots through out the leaf and not that nitrogen tipping you are seeing. good news is its not all the way up the plant yet. Flush that beast out and make sure your ph is in a good zone. cal mag lockout and ph fluctuations go hand in hand and often look the same. Corrective action: flush until a decent ph is reached. Double up on cal mag and a light nuet solution. Takes about 7 days to see if it has corrected. just watch the upper/newer growth for signs of it still being locked out IE spots or discoloration. good luck to ya. your pretty close to wrapping that grow up. CAL and MAG are both absorbed the best at a PH of 6.2