The degrees GH is a unit of German measure to indicate the total hardness.
The GH value is composed of dissolved minerals, mainly calcium and magnesium.
These elements are important not only for the health of the fish but also for plants. The optimal measure in the aquarium is between 7 and 12 degrees.
To reduce the total hardness in the aquarium we recommend a partial water change with demineralised water alone, but to increase the value you can use the SHG Amazonas salts or SHG Africa.