Grow Products Cal-Mag Max‚ contains 4% calcium and 2% chelated magnesium. Calcium and Magnesium are very important secondary nutrients for plants. They are a part of the chlorophyll molecule, which is necessary for sugar formation.Inadequate amounts of Magnesium will first appear as a general loss of green color at bottoms of older leaves (interveinal chlorosis).This is a 2-1/2 gallon container.