Black spots on leaves

scope under leaf for any tiny creepy-crawlies... Could be nute-related to. I'd get that pH up to ~6.8 or so in soil. That may fix the problem. Then re-assess. if it takes a major nosedive while maintaining regular fertilization and bringing pH up, obviously change course and disregard what i say. If they are reddish or rusty dots, it could be Mg deficiency... but you also need to rule out lockout from feeding too much of any p/k/ca/s. So, if yo know the ppms of what you provide you can make a more precise guess as to what course of action to take. get that pH proper first... solves a ton of problems on its own. Ensure no dry pockets when watering.. get it fully saturated and that takes a little runoff even if in soil. (soilless 20% runoff, full strenght nutes everytime -- i mention in case what i say has tunnel vision.. different ways of growing require slightly different practices at times)