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Carbonates (CO3-) are salts of carbonic acid (H2CO3) the most common which is found in marine aquariums is calcium carbonate. Dissolved carbonates also play an important role in pH regulation where it will act as a buffer to changes in pH by being the dominate component of alkalinity. Bicarbonates (HCO3-) can be consumed by marine algae during photosynthesis as a source of carbon.