cant see too good, but the spots seam to be inbetween the vains , fist is to check the ph of the water goin in then the run off from the pot, should be at about 6. then if they are try a flush then some calmag in the nute regimin, alot of the same problems are coming up in soil greowers lately, the brown black spot inbetween the leaves. this is a problem with either nute lock out, or calcium deficency. cause could be many things from soil to ph, to salt build up.