Brown spots and yellow leaves

There are some brown spots on some of my leaves and like 3 leaves on 2 different sets were completely yellow (as a bannana). I use fox farm nutes fyi. What could be wrong? this just started happening and i have been using fox farm for a while.

I have a problem, My problem is that on the main cola there are brown spots on a ton of the leaves. And I want to feed with fox farm one more time before i begin flushing with just water and molasses. But do these brown spots mean i am feeding too much, or are they natural, and i should be ok to feed them one more time???