yellow leaves at bottom of plants

leaves at bottom yellow. flushed yesterday. added nutes. how long till green again? pic included. 60 plant caffinated kush grow. auto flower . 1200 watts total hps. 36 sq. ft

you flushed then just gave it nutes agin? lol, you might have nute burn and your just reburning preety much. Anyway i would just flush again, it takes about a week to show signs of recover so give it time. Also if the veins are green it might just be a mg defficancy, mist some epsom/water mix on it or feed your soil some lime.