Your getting magnesium defficiency for sure as well as a little big of PK , the yellowing you can see is from the magnesium you see and the little brown spots that look like rust are from the PK , this is an easy fix all you have to do is adjust your nutrient solution to be more bloom oriented as well as add some CalMag to the mix . I would recommend you do a good PK boost in order to help your plant get back on track and to help it facilitate the fattening of buds . I would also recommend that you lower your PH abit to 6.6-6.8 this way you can ensure your plant wont get any locks outs in the medium . Although 6.9 isnt that much higher you would be surprised on what a 0.1 can do . Other then that you are well on your way to getting some nice medicine :) . I hope the information provided helps you on your quest to the finish line ! -Happy Growing!