double check your fert's label before changin pH. Mine says 6-6.5 for hydro. It depends on what the chemical composition is of what you feed...
the idea of the different pH's is to slow or increase rate of various nutes that would by otherwise less available in soil. A pH closer to 7 helps wiht N, but in hydro it is very available and would only aid in causing a toxicity of N at that pH in hydro.
so, it depends on your nutes. it's dangerous just to change pH if unsure... you could compound the problem.
Dark green.. marbling as in glossy? easy up on nutes portion of mix with the heavy K... its potassium? again, could be due to ratios of other nutrients, so it's something you have to investigate further before jumping the gun on anything.
i see cal-mag.. do your other parts supply that? you may be giving too much. you may also have already calculated this stuff out... sorry, if so, but it's important to note.