Reef Complete, 4 L / 1 fl. gal. Raises calcium and maintains magnesium and strontium A concentrated optimized blend of ionic calcium designed to restore calcium to levels found in natural seawater without affecting pH Calcium and carbonates are essential to all coral growth; If either become deficient, coral growth will cease followed by a rapid decline in health Also includes magnesium and strontium in amounts proportionate to typical utilization ratios; allowing one to maintain all three important elements 250 milliliters treats 1000 US gallons