Plants -- just like all forms of life, including human beings -- require a complete range of essential elements in order to thrive. Not one can be lacking, or your crops may suffer nutrient deficiencies. Of course, different concentrations of different nutrients are required by plants and animals at different stages of their lives. Just like young, developing children need vitamins and minerals, your plants need a steady supply of calcium and magnesium to ensure vigrorous, nutrient healthy growth. But even expert growers often overlook another crucial element for high-value crops: specific forms of irion in precise ratios. If you're using our base nutrients, your crops are already getting the correct amounts of Ca, Mg, and Fe. But if you're using our competitors' base nutrients, your crops could suffer from stunted growth or yellowing leaves. In that case, use Sensi Cal-Mag Xtra® -- the nutrient supplement formulated with the ratios of Ca, Mg, and Fe your crops need. As always, you're protected by our 100% money-back Grower Guarantee.