Tilapia Topic, Aquaculture Environment, Hardness

Total water hardness is a measure of the concentration of divalent metal ions, primarily calcium and magnesium in water. Dissimilar freshwater sources may have different water hardness. For example, rain water runoff in windward mountain streams often has low total hardness (e.g. < 15 mg/L). On the other hand, total water hardness may be 300 mg/L or more in even slightly brackish water.

Water hardness in aquaculture tanks or ponds changes little from that found in the source water and does not vary appreciably diurnally. At a particular site, knowledge of total water hardness is important and several measurements of the source water taken at different times of the year is indicated. An understanding of the hardness of culture is important as hardness may affect phytoplankton and fish productivity.