Carbonate Hardness/Alkalinity

Carbonates play a crucial role in the buffering capacity of aquarium water, which is known as alkalinity. Alkalinity is vital for maintaining a stable pH in your tank. Without adequate alkalinity, the pH will fluctuate, potentially stressing your fish and other aquatic life. This is because living organisms are constantly undergoing chemical reactions that affect the water’s chemistry.

Even for species that thrive in soft water, it’s still beneficial to have some level of alkalinity in the water. A stable pH is less stressful for fish than constantly fluctuating levels, which can cause health issues. For most freshwater aquariums, a carbonate hardness (KH) of 4-8 is ideal, while saltwater aquariums typically require 8-12 KH for optimal stability.

The Role of Carbonates in Aquarium Ecosystems

Carbonates are vital for invertebrates, as they rely on calcium, magnesium, and carbonates to form calcium carbonate. This compound makes up the skeletons of corals and the shells or carapaces of invertebrates. Since carbonates can’t be sourced from food, they must be absorbed from the water. This makes proper carbonate levels essential for maintaining a healthy aquatic ecosystem.

How to Adjust Carbonate Levels

Adjusting carbonate levels in your tank is similar to managing general hardness (GH). If you’re using Reverse Osmosis Deionized (RODI) water for water changes, it will naturally lower carbonate levels. On the other hand, if your tap water contains too many carbonates, you can blend RODI water with tap water to achieve the right balance once your parameters are within range.

To raise your aquarium's KH, the simplest solution is to add baking soda. For every 10 gallons of water, use 1/8 teaspoon of baking soda to increase the KH by 1°. This method can also help to raise your tank's alkalinity, as carbonates directly contribute to the overall alkalinity of the water.