Cal-Magâ„¢ Plus is a highly fortified calcium, magnesium and iron plant supplement formulated to correct common deficiencies. Supplementing your preferred nutrient program with Cal-Magâ„¢ Plus is strongly recommended when using reverse osmosis water and when growing in coco coir-based medias to compensate for natural calcium draw. Cal-Magâ„¢ Plus can also be applied as a foliar spray to further enhance growth.