Seachem Reef Carbonate is a concentrated (4000 meq/L) optimized blend of carbonate and bicarbonate salts designed to restore and maintain alkalinity in the reef aquarium. 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 carbonates (Reef Carbonate) and calcium (Reef Advantage Calcium or Reef Complete). Whereas competing products simply use sodium bicarbonate, Reef Carbonate is made with a blend of carbonate and bicarbonate salts. This blend of salts results in Reef Carbonate yielding a pK of roughly 9.0 in saltwater (higher than competing products). In a closed reef system, the multitude of organics produced by reef inhabitants tends to force pH downward, but the advantage of Reef Carbonate's higher pK is a stabilization of pH around 8.3-8.4. Competing products' formulations make them incapable of such a claim, so pH will always fall below desirable levels for a reef aquarium. Used as directed, Reef Carbonate will not deplete calcium, magnesium or strontium which usually tend to precipitate with increasing alkalinity. Reef alkalinity should be maintained at 3–6 meq/L (8–17 dKH). Alkalinity should not be allowed to fall below 2 meq/L. Comes in 500ml bottle.