"EPSOM SALTS ...But magnesium deficiency is not the only cause of leaf yellowing - a shortage of nitrogen can have similar symptoms, but this is MUCH less common as most of us routinely feed nitrogen-containing ferts. Some pests, such as red spider mite, can cause leaf yellowing, as can a whole host of viruses to which your ladies are susceptible. And don´t forget it is normal for the lowest leaves on the plant to yellow and die. They have done their job, and your buds are now being fed by the products of the photosynthesis being carried out by the fan leaves." Thanks to Spanishfly This Thread is titled EPSOM SALTS and should help a bit