I went back b/c I had the time to spare, and from what I see in your last posted pic is either P or K related. In my experience K def and P def look very similar except K starts at the leaf margins and P shows more in the middles of the leaf fingers. Either case, mid bloom is time to lower the N and bring up the P & K levels in the feeding. More specifically than FF Nutes, as I found a fair amount of products in their lineup, can you specify which bottles you're using, which grow medium and what was the exact mixture recipe you last mixed up? As in ml/gal, tsp/gal, TBLS/gal etc.