Nitrogen deficiency in cannabis
What it looks like
Yellowing starts on the older, lower leaves and moves up. The plant looks pale green, then yellow, and growth slows. Veins can yellow with the leaf, which separates it from magnesium.
What usually causes it
Check that the plant is actually hungry before you raise feed. A pale plant in a wet pot is often roots, not an empty bottle. If the medium is dry and the pH is in range, a normal grow feed is the correction. Soil likes about 6.0–6.5. Coco and hydro sit lower, about 5.8–6.2.
Check this first
Pale from the bottom up, old leaves yellowing and dropping. Check that you are actually feeding, and that the runoff pH is in range. A plant in a hot pot can look hungry because the root is locked, not because the bottle is empty.
This is identification for a home grow. It is not a pesticide label and not medical advice. Follow your local law.