My leaves are turning yellow see photos day 19/21 ...

A cannabis iron deficiency is usually seen first on bright yellow new leaves, and the symptoms of a cannabis iron deficiency can sometimes appear alongside other cannabis nutrient problems or deficiencies. An iron deficiency is usually caused by problems with pH, though sometimes a cannabis iron deficiency can be triggered by a stressful environment and may clear up on its own after the period of stress is over. In soil, iron is best absorbed by the roots in the 6.0 – 6.5 pH.