Someone help. Unsure of defiency!

My plant is in soil and is in the 3rd week of flowering (monkey pal- a afghani #1 x durban poison) a good majority of the fan leaves are having the same problems as the leaf in the pic below. I've researched but still not sure whats wrong, if someone would help me out that'd be great. thanks




http://https://www.rollitup.org/marijuana-pics/index.php?n=6412