Dead and spotty leafage at 5 weeks flowering

Well as the title says i've got some dead and spotty leafage on my plants, its affecting one of the plants the most however the spots which were the first signs of decay are appearing on all three. Im not sure whether it is something i have to deal with or can live with. heres some pics of the grow and the offending leafage. Would love to get some clarification on this, its my first grow aswell so i dont know much at all.