It's at about this time in a grow when all plants start needing a whole lot more P and K and less N than you've been giving during veg.... What this is showing is a pretty good P&K deficiency (mostly a phosphorus deficiency) perhaps brought about by a nitrogen toxicity which has locked out those other terribly important nutes. I have no idea what it is exactly that you're feeding but the NPK ratios ought to be about 1-5-4 ... your EC is good, could/maybe SHOULD be higher ... and your pH is also good - just juggle around with the ratios.
Good luck.