Reef Complete is a concentrated (160,000 mg/L) optimized blend of ionic calcium designed to restore and maintain calcium to levels found in natural seawater without affecting pH. Calcium and carbonates are essential to all coral growth. If either becomes deficient, coral growth will cease, followed by a rapid decline in coral health. To prevent this you must provide calcium (Reef Complete) and carbonates (Reef Builder or Reef Carbonate). Reef Complete also includes magnesium and strontium in amounts proportionate to typical utilization ratios (100:5:0.1, Ca:Mg:Sr). This allows one to maintain these two important elements while maintaining calcium. 250ml.