Cal-Mag Plus is a highly fortified calcium, magnesium and iron plant supplement formulated to correct common deficiencies. Supplementing your preferred nutrient program with Cal-Mag Plus is strongly recommended when using reverse osmosis water and when growing in Coco Coir based medias to compensate for natural calcium draw. Cal-Mag Plus can also be applied as a foliar spray to further enhance growth. Some sizes may not be stocked in all locations. Item will not ship UPS. Must ship on a pallet flat rate only.