Royal Critical auto

Hey Growmie, I would say this is a light problem this looks more like a Phosphorus deficiency. Phosphorus deficiencies exhibit slow growing, weak and stunted plants with dark green or purple pigmentation in older leaves and stems. Some deficiency during flowering is normal, but too much shouldn't be tolerated. That would be why the lower leaves are so dark green, they would be considered the older leaves and stems. If you do want to go ahead and rule the light also just back it off a few inches and that should fix your worries of it being light burn. I hope this helps and remember ..."Happy Growing" and "Free your mind one puff at a time".