Carbonate Hardness of Water (KH)

Last Updated: August 14, 2017

Definition - What does Carbonate Hardness of Water (KH) mean?

The carbonate hardness of water, also known as carbonate alkalinity, refers to how the alkalinity of water is measured.

A water supply's alkalinity is caused by a combination of carbonate and bicarbonate anions being present in varying degrees.

Carbonate hardness is commonly referred to as KH. The ‘k’ is garnered from the German word for carbonate, which is karbonatharte.

Sometimes, the term carbonate hardness can be a synonym for 'temporary hardness'. In this case, carbonate hardness refers to the portion of hard water that can be removed by using processes like boiling or adding lime-based water softeners.

MaximumYield explains Carbonate Hardness of Water (KH)

Water test kits are widely available at stores and hydroponic suppliers that measure the carbonate hardness level of water. The test kits are usually found by the aquatic supplies.

Carbonate hardness measures the water’s alkalinity and provides an idea of the water’s buffering ability/capacity. The alkalinity level shows the water’s ability to absorb and neutralize acid. If the water’s alkalinity is high, then the pH level tends to be fairly stable and less prone to swings. A high carbonate hardness level stabilizes the water.

Many people mistakenly believe that the carbonate hardness and general hardness of water are related and virtually the same. However, both are distinct and in many instances, a water test's results will reveal that they are actually far removed from each other. In some areas of the world, the water’s carbonate hardness level is higher than the general hardness level.

The carbonate hardness level of water in ponds and aquariums is very important for the aquatic life that resides in the water. Fish and other aquatic life usually require a stable pH to thrive. Some fish, turtles, snails, and other aquatic lifeforms are very sensitive to water pH swings and will perish quickly without stability – the same goes for plants in an aquaponic system.

Carbonate hardness is also an important consideration in hydroponic growing systems.

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