Black stains on leaves

that's just a continued progression of nitrogen deficiency... ignoring the palling that started at the bottom and crept upward is the cause. increase concentration of N by some proportion... do it without changing other elements of fertilizer too drasatically. Though there are some other symptoms present, they are a bit ambigous to diagnose from pictures alone. (tip symptoms on the leaves not afflicted with N-def as of yet)

Use a search engine to look for nitrogen deficiency, magnesium deficiency, potassium deficiency, phosphorus deficiency, manganese deficiency. Compare pictures and description of how it starts to see which one fits the problem your having.