BioBudsanswered grow question 4 years ago That is a magnesium deficiency, i see the tip of this leave pointing down, which suggests watering issue. But... Hard to tell w/o seeing whole plant and situation. So could be too much water, could be not feeding calmag while growing under LED, could be PH that is too high or low, preventing this. Let soil dry, do a foliar spray with some calmag.