In normal seawater or marine aquarium water, the bicarbonate greatly dominates all
other ions that contribute to alkalinity, so knowing the amount of H[SIZE=-1]+[/SIZE] needed to reduce the pH to 4.5 is akin to knowing how much bicarbonate is present. Aquarists have therefore found it convenient to use alkalinity as a surrogate measure for bicarbonate.
One important caveat to this surrogate measure is that some artificial seawater mixes, such as Seachem salt, contain
elevated concentrations of borate. While borate is natural at low levels, and does contribute to
pH stability, too much interferes with the normal relationship between bicarbonate and alkalinity, and aquaria using those mixes must take this difference into account when
determining the appropriate alkalinity level.