Alkalinity is an indirect measurement use to check for the presence of bicarbonate in the water. Maintaining an optimum alkalinity value or level in a saltwater reef aquarium is very important as most corals and invertebrates get their carbon source from the bicarbonate in the saltwater. This carbon is needed in the building of their calcium carbonate skeleton for their healthy grow. Since bicarbonate is constantly absorbed from the saltwater, the alkalinity value tends to drift to the lowers side over time. As such, it is important that the alkalinity value are monitored periodically so that supplement or additive can be added to maintain the value at between 2.5 and 4 meq/L or 7-11 dKH or 125-200 ppm of dissolve bicarbonate. Visit this page for more information about alkalinity and how to control it in the saltwater reef aquarium.
The easy and simple to use alkalinity checker from HANNA