MAGNESIUM AND SULFUR BOOST
Magnesium deficiency is the MOST common cause of poor yields besides overfeeding. The primary symptom of Magnesium deficiency is premature yellowing or interveinal fading of leaves. Sulfur deficiency is characterized by the fading of the veins. Once yellowing is visible, CO2 consumption has slowed. That affects flower development.
CAL-MAG IS NOT THE ANSWER
Soil/Hydro: Use 1 tsp (5ml) per gallon of water throughout the flower cycle.