Brown spots on the leaves

Hey Growmie, I would say, seeing as your plants are in flower, the rust spots and dark leaves (if it is older growth and older leaves) are phosphorus issues. The lighter leaf with the spotting ( if it is newer growth, or closer to the light, could be a calcium issue. I’m leaning towards your plant cannabilizing itself in search of phosphorus for bud growth. It really looks for it early in flower land can show those signs in older growth. As long as your PH runoff is on point, I would start with using both phosphorus and calcium.

Could be a calmag deficiency