A concentrated (50000 mg/L) bioavailable polygluconate complexed calcium intended to maintain calcium in the reef aquarium without altering pH (formulated at pH 8.2). Polygluconate complexation confers several benefits: it increases the bioavailability of the calcium it provides a rich source of metabolic energy to help maintain peak coral growth and it inhibits calcium precipitation/alkalinity depletion. One side benefit includes enhancement of denitrification. Polygluconate contains no nitrogen or phosphorous thus it is biologically impossible for it to lead to algae growth in a properly maintained reef system. Reef Calcium™ may be used alone to maintain calcium but will provide enhanced levels of coral growth when used in conjunction with an ionic calcium supplement (Reef Complete™ Reef Advantage Calcium™ Reef Kalkwasser™). Reef Calcium™ is intended to maintain calcium levels; if calcium becomes seriously depleted one should either perform a water change or use an ionic calcium supplement to restore the depleted level of calcium. Each 100 mL treats up to 1600 L (400 gallons).