JBL Aquaristik und Terraristik GH test set

Depending on the origin and composition of the substrate, water can contain varying amounts of alkaline earth salts. Typically, these are calcium and magnesium salts. The total amount of calcium and magnesium ions represents the overall hardness. Most fish and plants can be successfully maintained at an overall hardness of about 8-20°dH. However, one should strive to reduce excessively high overall hardness values through appropriate measures.