NT Labs Test Hardness (GH / KH) is an aquarium water testing kit used to measure General Hardness (GH) and Carbonate Hardness (KH) levels in freshwater or marine tanks.

What is GH and KH?
General Hardness (GH) measures the amount of dissolved minerals in the water, mainly calcium and magnesium. These minerals are important for fish health, osmoregulation, plant growth, and the development of shrimp and snails.

Carbonate Hardness (KH) measures the level of carbonates and bicarbonates in the water. KH acts as a buffer that helps stabilise pH and prevents sudden pH swings, which can be stressful or harmful to fish and aquatic life.

Both GH and KH are invisible to the naked eye, making regular testing important for maintaining a stable aquarium environment.

What are the recommended GH and KH levels?
The ideal GH and KH levels depend on the type of fish and plants being kept.

For most tropical freshwater aquariums, these are the ideal settings:

• GH: 4 – 12 dGH
• KH: 3 – 8 dKH

Soft water species such as discus or certain tetras may require lower hardness levels, while African cichlids and livebearers generally prefer harder water conditions.

What do I do if the GH or KH level is wrong?
If GH or KH levels are too low, mineral supplements, crushed coral, or hardness buffers can be added gradually to increase hardness and improve water stability.

If GH or KH levels are too high, partial water changes with softer water or reverse osmosis (RO) water may help reduce hardness levels safely.

Sudden changes in hardness should always be avoided, as rapid fluctuations can stress fish and plants.

How to use?

- Ensure the test tube is clean.
- Take a 5 ml sample of water into the test tube.
- Add 1 drop of the GH or KH reagent and shake gently.
- Continue adding drops one at a time, shaking after each drop, until the colour changes completely.
- Count the number of drops used before the colour changes.
- The number of drops added equals the GH or KH level in degrees of hardness (dGH / dKH).
- Rinse the test tube thoroughly after use.