Key Parameters - Water Hardness

Water hardness is similar to alkalinity but represents different measurements. Hardness is chiefly a measure of calcium and magnesium, but other ions such as aluminium, iron, manganese, strontium, zinc, and hydrogen ions are also included. When the hardness level is equal to the combined carbonate and bicarbonate alkalinity, it is referred to as carbonate hardness.

Hardness values greater than the sum of the carbonate and bicarbonate alkalinity are referred to as non-carbonated hardness. Water hardness is inextricably linked to a waters ‘buffering’ capacity.

A buffering capacity is essential in aquatic systems that are to support healthy and viable fish populations as well as many other aquatic life forms. It is essential to avoid wide swings in pH.

Without some means of storing carbon dioxide released from plant and animal respiration, pH levels may fluctuate in ponds from approximately 4-5 to over 10 during the day. Calcium carbonate can achieve this by binding with the H+ ions. Generally speaking the greater the water hardness the more buffering capacity available in the water. Hardness values of at least 20 p.p.m. should be maintained for optimum growth of aquatic organisms.