Looks like calcium deficiency; if those plants have been in the same pots for over 5 weeks, it's likely the lime is used up and the pH is dropping too. You should check the runoff pH, and use calmag with your fertilizer, especially if you see your pH is low.
You've got to give more info like about your fertilizer and all that for a diagnosis.
stinkyattic Reviewed by stinkyattic on . why R this plants leafs yellowing?.... what can I do to make the yellowing stop so the new growth don't turn yellow. and is she gunna make till harvest. it'll be a 12-14 week flowering cycle cuz she is a sativa. so what can I give her to help the yellowing? Rating: 5