Hardwater Flora Micro by General Hydroponics is designed grow areas where the tap water is over 200 ppm (or contains Calcium above 70 ppm). Also, if your water contains 30 to 50 ppm Calcium, you can mix our original Flora Micro® with Flora Micro® Hardwater to create a perfect Micro blend for your plants. Flora Micro is the foundation of the "Building-Block" system. It provides plants with Nitrogen, Potassium, Calcium and trace elements. Combine with Flora Gro® and Flora Bloom® for increased results. Great overall supplement for a variety of plant types! Quantity: 15 Gallon.