WTF is wrong with leaves.??

I need to know wats causeing this problem...Leaves are turning yellow an falling off my plant....Its starting from the older bottom fan leaves an moving up

pictures would help

sounds like N deficiency but yeah, would need pics or at least more details

pics please?

Pics would help but so would ANY information about the grow...whether it's in veg or flower, etc. Lazy post, search the forums before posting, might save you some time.