Brown spots and yellowing leaves.

If you have been adding cal/mg every feed, you likely have some lockout going on. Check your runoff water for the ec and ph. If your ec is gone overboard, the cal/mg is likely the cause. Very little needed in the soil once they start to bud. Check the ph as well. If this is out then it also creates lockout. It is definitely not a defficiency my friend, well it is but caused from locking out the roots. Cal/mg has lots of nitrogen as well and that is something the girls don't need much of once in flower. Cheers