Can someone tell me what this is being caused by? My suspicion is a potassium/ calcium deficiency? It's affecting mostly the larger fan leaves. Also, affected leaf stems are turning purple. Posted a pic of one of the leaves
Could be a potassium deficiency. Check your runoff waters ph and ec levels to know for sure. Ph out, lockout, ec to high lockout. Ph and ec both ok for flower time , then you have a deficiency.