you'll probably only see mag def, or cal and mag def; low ph isn't too big a deal until you get down in the low fives. there's an organic product available called cal/mag, made by botanicare. it works wonders for cal and mag problems, regardless of ph (hydroponic fertilizer).
my dirt starts at 5.0.... my babies go yellow fast, magnesium def. 10ml per gallon cal/mag makes them green again.