It is hard to diagnose w/o pics but I ust recently dealt with a TOTALLY surprise Ca problem which I heard was widespread among growers on the same city water as I'[m on... We get our water from a river and it is swollen and diluted with snowmelt.. First time I have EVER seen it. But you need to determine your soil's pH anyway.
Calcium def will show as necrotic blotches and if you are taking clones, it's easy to mistake for rot actually.
CalMAg Plus is your best bet. Also fish emulsion contains calcium.