the spots are located on a number of leaves in my case. only on the lower leaves though.out of 20 girls i just found a leaf that looks just like that. its just one leaf on one plant. i add cal mag with their feeding so i doubt thats it.
This just happened to mine, it was caused by a build up of nutes effecting the ph. Do a good flush with ph'ed water of 6.5 and start over with half nutes after 4-5 days. thats what im doing now. good luck.the spots are located on a number of leaves in my case. only on the lower leaves though.