Sativa-dominant auto's

Nice growth from last week. I'm completely shocked. Apparently the grow light is massively more effective than depending on the sun this time of year. And to think 2 weeks ago I was really disappointed and thinking these were about ready for harvest. Don't think I'll ever depend on the sun again for growing. Haven't been measuring horizontal growth, but Amnesia Haze finally grew another inch vertically to be 6 inches now, and Bruce Banner is 12 inches now. Bruce Banner still looks pathetic compared to the others that I'm growing under the same conditions, but it still has shown a lot of improvement from last week. Noticed some of the leaves starting to turn yellow. I raised the grow light to be as close to the ceiling as possible, in case it was light burn, but the leaves toward the bottom seemed to be turning yellow first which leads me to believe it instead cold be 1) natural because these will be ready to harvest soon, or 2) a nitrogen deficiency. These are in 5 gallon pots of Fox Farm Happy Frog soil, which is already nutrient rich and probably an overkill size pot for auto's, so I'm thinking it's NOT a nitrogen deficiency, but just to be safe I started adding Fox Farm Big Bloom at 1/4 the recommended strength every other watering.