Sodium hydroxid (NaOH), sodiumb bicarbonate (NaHCO3) or sodium carbonate (Na2CO3) can be used to adjust the alkalinity and pH. Powedered limestone [calcite or calcium carbonate (CaCO3)] is not recommended because with time, the calcium in the lime may change the ratio of major cations (Breder and Smith 1932). Cooper (1932) reported that at the Plymouth Aquarium in England the addition of lime to maintain pH eventually increased the calcium concentration in the water to 0.62 g/l compared with 0.39 g/l in the seawater directly offshore.
Sodium, the predominate cation in seawater, can be added as carbonate or bicarbonate salts for longer periods before the cation balance is upset. Breder and Smith (1932) estimated that if all thebicarbonate ion in seawater at the New York Auarium were to be replaced over a period of 2.5 years with sodium bicarbonate, the sodium level would increase a mere 0.5%. If lime were used instead, the calcium level would increase by 10%, or 20 times the molar concentration of calcium in offshore seawater.