Calcium is not the only substance needed to form the skeletal material of corals and allow calcareous algae to grow. Carbonate and bicarbonate are also needed and these two substances can have a major effect on stabilising or buffering pH levels in the aquarium in the correct range of 8.1 to 8.4. The total carbonate and bicarbonate concentration is also called alkalinity or carbonate hardness and for a stable system the alkalinity should not fluctuate by more than 5% from the optimum level of approx. 2.8 meq/L i.e a maximum fluctuation of 0.14 meq/L. The Salifert test is sensitive enough to detect small changes in levels of alkalinity, measuring in steps of 0.1 meq/L and demonstrating a very sharp colour change. The Salifert KH + pH buffer additive makes correction of the alkalinity or carbonate hardness simple and does not upset the pH of the system. Sufficient for 100 to 200 tests.