The terms alkalinity and hardness are often used interchangeably when discussing water quality.  This is because most hardness and alkalinity comes from limestone or dolomite sources in nature. When water passes through the rocks contain limestone (calcium carbonate) and dolomite (calcium and magnesium carbonate) in the ground picks up minerals on the way. When limestone and dolomite dissolve in water, one half of the molecule is calcium or magnesium (the "hardness") and the other half is the carbonate (the "alkalinity"), so most of the times they are equal. However, they are very separate measurements, and have very different importance for the aquarium. Total alkalinity and total hardness together with salinity and dissolved solid are defining characteristics in assessing the quality of water. Although aquaculturists frequently measure concentrations of these two variables and manage ponds to maintain adequate alkalinity and hardness, few have a clear understanding of what they are measuring and managing. This possibly is because alkalinity and hardness are not actual dissolved substances in water, but they are indices of concentration of groups of variables that influence water quality and production of culture species. Therefore, the purpose of this paper is to explain the sources, measurement and important of total alkalinity and hardness of culturing water.