Cal/Mag is really easy to tell between when its advanced. I still feel that you have a calcium def, not mag. HOWEVER! There's no good goddamn reason to not add those epsom salts AND calcium sulfate. People refer to it as "a cal/mag problem" because the symptoms are closely related. If you got a local growshop or greenhouse, check out cal/mag. Its going to be your absolute best option. If you'd rather track down gypsum and epsom that'll work too, I don't know how much gypsum to use per gallon. If you can't find gypsum, most farm stores have hydrated lime. You'll have to buy 50 pounds but its only around 7 bucks. Hydrated lime works like any other lime except its water soluble. Don't use too much, but watering with that shit will beef up minerals and instantly bring the pH of your soil to neutral. The lime bazooka if you will.
Posted this on some thread where a dude was swaggering about how badass stealing electricity is, then I remember how awesome office space is -
http://www.youtube.com/watch?v=8u84d7nY8pQ
Riiiight.
but of course I'm just joshing ya!