The Salifert KH/Alk (Carbonate Hardness/Alkalinity) Profi‑Test is a test kit designed to measure the alkalinity (KH) or carbonate hardness of aquarium water. It is widely used in marine and reef aquariums to monitor the buffering capacity of water and maintain stable conditions for corals and other marine organisms.

The Salifert KH/Alk Profi-Test measures the total concentration of carbonate and bicarbonate ions, which together are referred to as alkalinity or carbonate hardness (KH). These components play an essential role in stabilizing aquarium pH levels, typically keeping them within the optimal range of 8.1–8.4 in reef aquariums.

Alkalinity is critical for the growth of corals and calcareous algae, as it provides the carbonate ions required to build their skeletons. If alkalinity levels fluctuate too much, coral growth can slow and the aquarium’s pH stability may be affected.

The kit uses a titration method with a color indicator, allowing hobbyists to detect even small changes in alkalinity with a clear color transition during testing.