Hey Growmie,
Brown spots on fan leaves during flowering hint at a potassium shortage; other signs include: Pale and discolored foliage. Stunted and abnormal growth. Leaves curling upward. Feel free to shoot me a holler if you ever need any help, I'd be honored to assist you. Hopefully, this was helpful, and remember ... "Happy Growing" and "Free your mind one puff at a time".