What's Carbonate Hardnesse kH?

kH (Carbonate Hardness) plays a key role in the pH of the water in your aquarium. kH is a measure of carbonate and bicarbonate ions in the water column. These ions act as a natural regular and buffer pH fluctuations. A higher kH would allow for a more stable pH for the critters and fish in the tank. In a planted aquarium, pH would fluctuate due to carbon dioxide (CO2) and Oxygen (O2). At night, when there is no light, pH will decrease and become more acidic as the co2 forms carbonic acid in the water. When there is sufficient lighting, pH will increase, as oxygen dissolves in the water. While these fluctuations do occur in fish only aquariums, they occur more in aquariums where there is plant mass (this includes macro algae in saltwater aquariums).

KH testing with the API test kit works by adding drops of the liquid into a test tube of 5ml of water and counting the number of drops required to turn the water yellow. The number of drops is the degree of kH the water is at. RO water is less hard at 1 degree, while tap water is usually around 5 degrees. On degree of kH is equal to 17.9 parts per million (ppm). It is preferable to use RO water in systems in which substrate is used to reduce pH. A high pH will reduce the effect the substrate has in decreasing pH or increasing pH. This will also result in a lower life span of said substrate used to change the pH.

It is important to consider the requirements of plants, fish, critters, corals to determine the degree of kH the water needs to be at. Water with no kH present will result in irregular result of pH, as without any buffer pH will drastically fluctuate. This often results in a lot of aquatic deaths of fauna. Aquatic plants are usually resilient to these changes and are able withstand these changes. However, there are sensitive species of aquatic plants that cannot tolerate such fluctuations. It is much safer to keep the pH stable.

Here are a few reasons why kH might fluctuate on their own

· New water introduced may have a higher or lower kH level that currently present
· Nitrifying Bacteria also consumes kH, thus lowering pH over time
· Certain substrates and generate kH in your tank to keep it stable, but after a long period the effectiveness will usually go down
· Water agitation can also break down carbonates in the water, lowering kH

How to raise kH
· Pure Baking Soda (sodium bicarbonate)
o It will raise pH and kH
o One teaspoon (15 ml) in 50L (13 gallons) will raise kH by 4 degrees
· Crushed Corals will increased kH without affecting pH

Final Notes
RO water or clean rain water will have 0 kH and can help reduce the kH in your aquarium. Be careful when using rain water as it does pick up pollutants from the air or the rain gutters connected to your rain barrel. Also, boiling water can be used, however it can get quite expensive to boil large volumes of water and waiting for it to cool can be a daunting process.