What the term acid binding capacity (SBV) stands for
The acid binding capacity is a measure of the buffering capacity of water, measured by titration with HCl based on a pH of 4.3. The acid-binding capacity is the water value, which is measured in aquaristics using the so-called KH test. SBV in mmol/lx 2.8 gives the KH used in aquaristics in numbers. However, the KH term used in aquaristics is outdated.
Outside of aquaristics, the carbonate hardness is defined as the amount of alkaline earth ions that are charged with an equal amount of hydrogen carbonate. This value is e.g. B. useful to determine the content of phosphates and zeolites in water, e.g. B. to prevent washing machines from calcifying.
When heated, bicarbonate with the same amount of calcium and magnesium precipitates as lime, excess bicarbonate, i.e. bicarbonate for which there is no corresponding calcium or magnesium, remains in the water.
According to this definition, the carbonate hardness can never be greater than the total hardness, which is defined as the amount of all alkaline earth ions. According to this definition, the hydrogen carbonate, for which no alkaline earth ions are available as charge partners, does not contribute to the carbonate hardness. However, the carbonate hardness defined in this way is not interesting for aquaristics.
The total amount of hydrogen carbonate, which determines the buffering capacity of the water, is important for aquaristics. This is how CO2 reacts e.g. B. with the total amount of hydrogen carbonate and not just with the subset of hydrogen carbonate, for which alkaline earth ions are present as charge partners. The amount of all bicarbonates is therefore required to calculate the CO2 content in the water using the formula CO2 = KH x 10. In addition to calcium and magnesium, there is also sodium and potassium bicarbonate.
Plants also produce the carbon they need during bicarbonate assimilation from the total amount of bicarbonate and not just from the amount of bicarbonate with matching alkaline earth ions. Lime will precipitate as long as calcium and magnesium are present. If all of the calcium and magnesium has precipitated, lime can no longer precipitate, but the assimilation continues until there is no more hydrogen carbonate.
This “aquaristic” carbonate hardness can be greater than the total hardness. In this case there is more hydrogen carbonate than alkaline earth ions available.
If the water is hardened with agents such as KH-plus with potassium and sodium bicarbonate, the KH value used in aquaristics increases, while the KH value used outside of aquaristics does not increase.
Since the term acid-binding capacity has not yet become established, the term carbonate hardness is still used in aquaristics.