Seachem Reef Calcium is a concentrated (50,000 mg/L) bioavailable polygluconate complexed calcium intended to maintain calcium in the reef aquarium without altering pH. 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 prevents calcium precipitation/alkalinity depletion. Polygluconate contains no nitrogen or phosphorous, thus it is biologically impossible for it to lead to algae growth in a properly maintained reef system. Seachem 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 (Seachem Reef Complete, Seachem Reef Advantage Calcium). Seachem 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. 250ml.