From my experience growing in hydro, which is a bit different albeit the same idea, adding silica was one of the best things I did to my grows.. The stalks got thicker, foliage was more firm and stems had a distinct snap.. A lot of times, I would use extra silica to raise my pH if it was on the low end, instead of using something like pH UP or another base.. I never saw ill effects of using full strength silica on autos, as it was one of the few nutes that I could use at that level.. You leaves look similar to a pH shift which could be indicative of a little nute burn.. Then again, I've had some issues with the last couple grows of KS, towards the end the plants seemed to fall on their face and I seemed to have deficiencies regularly.. You could top-dress w/ some EWCs and/or some more KS to see if that helps..