<doh> Sorry, I thought you said you were adding molasses and calcium, which sounded fine. Molassest has some calcium, but have never heard it used for corrections.
WHFoods: Blackstrap molasses
Are you letting the soil dry out properly between waterings? I've seen spots like that, on plants with overwatering problems. I ran out of perlite a ways back, and had just got a 15 lb box of worm castings, for ammending the soil. (not as the medium itself, lol) Made a muddy mess that was a bitch to keep on a regular feeding/watering schedule. Ended-up with minor root rot but finally figured it out after transplanting to better soil mix.
Just a thought.