Have you looked under the leaves? This is most likely an insect issue as opposed to a nutrient issue! Spinosad is the most effective (and it's organic) at controlling thrips, leafminers, spider mites, mosquitoes, ants, fruit flies... so you really don't have to identify exactly what bug you're dealing with! You can use it either as a spray or you can get it into your soil (where a lot of bugs live) ... but best you get on top of this before too long!
Good luck!