if you havent fed it and its dry FEED IT!
ok so i measure my nutes per liter so 3.8L=1 gal... i give my girls at this stage about 3ml/l of cal mag... now i use Botanicare CalMag+ and full strength is 4-5ml/l
you are giving yours 1ml/l as autos get closer to flowering they require more CalMag (that is a fact)
hence why you are seeing a Calcium deficiency... i would double your cal mag... these rust spots wont go away but what you are looking for is signs of it slowing down and then not showing up anymore...
DONT WORRY DR. TRIP IS IN THE HOUSE MY FRIEND