The black spots are bug shit. Mites, or whatever, you need to work on pest control. 3 steps I would take after washing the leaves with dish soap as suggested. You can just wash them once, then:
1) sprinkle diatomaceous earth on the surface of the soil. This kills insects that live, breed, or land on the soil.
2) mist the plant with neem oil. This kills mites if you have them and protects the plant from further attacks from any insect.
3) put yellow sticky traps around your plants to monitor if the pests come back.

BTW that damage looks like thrips, not mites. Mite damage can be most pronounced on the upper parts of the plant, and the chew spots are smaller. Thrips breed in the soil and munch on low leaves, and you can see bigger chew spots. That looks like thrips. So the diatomaceous earth is your best bet.
stinkyattic Reviewed by stinkyattic on . black spots on leaves, wtf just a quick quesion, what the hell? Rating: 5