AF KH Pro (1000ml) by Aquaforest is a liquid supplement designed to stabilize and maintain the carbonate hardness (KH) levels in reef aquariums. KH, or alkalinity, is a crucial parameter in marine aquariums because it helps buffer and stabilize the pH, preventing harmful fluctuations that can stress corals, fish, and other marine organisms. This product is ideal for those who want to precisely control and maintain the alkalinity levels in their reef tanks.