For most of my grow my Granddaddy Purple plants have been looking healthy, though when I first transplanted them and moved them to the grow tent brown marks appeared on the lower leaves. Over the past few days the leaves towards the bottom have been yellowing increasingly. So far I’ve been using FoxFarm nutrients Grow Big and Big Bloom (as per the nutrient feeding schedule) Mixed with 6.0- 6.5 pH water. After doing some research yesterday a nitrogen deficiency seems like a likely culprit, so in the meantime of finding a solution I watered with approximately 6.7 pH water with not nutrients in case it was nutrient lockout. Yellowing still seems to be occurring when I checked on them today.
What might be wrong with my plants and how can I fix them?