KH value

The carbonate hardness or KH value, is an important pillar in the pond environment. The KH value is called temporary hardness. It is also referred to as the acid-binding capacity.
Carbonate is created by binding free carbonic acid (CO2) to calcium and or magnesium. It thus forms a carbonic acid (CO2) source for aquatic plants and algae. When the environment (microorganisms) releases enough CO2 to cover the needs for plant growth, the KH value will remain stable. However, when the plants’ need for CO2 exceeds the supply, the CO2 source from the carbonate will be tapped and the KH value will drop. A good KH value lies between 6° and 10°dH. A simple test can also be used to determine this value.

When the development of the pond environment stagnates, the KH value will decrease which is accompanied by an increasing pH. In contrast, when free carbon dioxide increases, the KH value will increase and the pH will decrease. We see this especially in the fall and winter when aquatic plant growth slows down or stagnates. Indeed, there is then a diminishing decrease in C02. This natural process of carbonic acid fixation prevents acidification of the environment and prevents oxygen depletion. By the way, carbonic acid can only bind if the GH value is sufficiently high, above 8 °dH.

In new ponds, as well as stagnant ponds, it may be necessary to increase the carbonate hardness. Special agents are available for this purpose that increase carbonate hardness over a long period of time.