yup lockout starting.. I have a few ladies in flower going right now, And I slipped up on my ph meterings and it did the EXACT same coloring. It does it on random leaves right? Mainly on the top of the plant, near the buds?
use a 1/4 tp of baking soda in a gal of water. Use that for a few days, and WATCH YOU PH. You dont want to get about 6.8 or so. And Give her some CAL-MAG. Those rust spots a tell tale sign your ph has gotten too low, and what causes it is the Calcium and Magnesium i no longer being absorbed.