Features:The total hardness (GH) indicates the quantity of magnesium and calcium salts dissolved in the water. If the amount of these salts is small, we speak of soft water, in the case of larger quantities of hard water. Usually the indication is in German degrees of hardness (°dH), where 1 °dH equals 10 mg per liter of calcium oxide (other units see table).
The concentration of these salts in the water influences the organic functions of fish and plants and for this reason must be checked regularly.
The optimal value for the total hardness depends on the fish species.
Many African (e.g. Aphyosemion) and Southeast Asian (e.g. Trichogaster) species tolerate hard water well. For example, South American characins need fresh water to stay healthy. In a
freshwater aquarium, a hardness of 3 -10 °dH is considered favourable.
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