Calcium is important for the plant's growth,it helps provide structure to the plant,especially under LED growing.
Signs of Calcium Deficiency
Upper leaf issues show spotting first
Lower leaves curl and twist
Yellow, brown spots appear on leaf and tips
Flower development is slow
Brown or dark spots on leaves
Random pattern of spots
Stems start to become weak
Roots become weak or begin to die
Correct the PH level for your growth.Soil, 6.0 - 7.0 pH range. Hydro or coco coir, 5.5 - 6.5 pH range.
Add extra calcium,some growers use tap water with great success! Most tap water contains calcium and magnesium in small quantities.