The GH value is an expression for the total hardness of the water and is formed by the salts of Magnesium (Mg) and Calcium (Ca) dissolved in the water. These minerals occur in rock but are dissolved by the water. Hard water can be found in many places within Europe, ie water with a lot of dissolved Ca and Mg salts. But there are also areas in Europe with relatively soft water. Also in the tropical areas where aquarium fish often come we find areas with hard water (Lake Malawi and Tanganyika) and areas with soft water (South America).
Calcium and Magnesium are very important from a biological point of view. Firstly because both substances stabilize the water values and secondly because they are important nutritional minerals for plants and animals. Because the fish, depending on their origin, are adapted to high or low GH values, the water in the aquarium must be adapted to their needs. Especially for the breeding of some fish, the hardness is very important.
The most common unit to represent hardness is German Hardness. 1 µdGH corresponds to 10 mg Calcium oxide dissolved in 1 l of water.
Due to the consumption by plants and animals, the Calcium and Magnesium content in the water is decreasing. Calcium and Magnesium salts are also consumed by the binding to phosphates and silicates. In contrast, various decorative stones or filter materials increase the GH value. Stones that increase the GH value are, for example, Carrara stones, marble or tuff. Topping up the evaporated water with hard tap water also increases the GH value because dissolved salts do not evaporate, but remain in the water.
Adjusting the GH value
It is easier to increase the GH value than to decrease it. HS aqua GH-Plus contains magnesium and calcium salts and can easily be added to the water until the desired GH value is reached. Calcium-containing decoration and filter materials can also increase the hardness. Such materials are, for example, Carrara pebbles and marble chips. Lowering a hardness that is too high is more difficult. This can be done by mixing the hard aquarium water with softer water. Softer water is available, for example, from Reverse Osmosis devices or with the aid of cation and anion exchangers.
|Aquarium type||GH value||Typical fish|
|South America aquarium||1-3||Discus, Tetras, Dwarf Cichlids, Various Catfish|
|asia aquarium||3-6||Barbels, loaches, labyrinth fish|
|West Africa Aquarium||3-6||Congo Salmons, West African Cichlids|
|Malawi lake aquarium||8-14||Malawi cichlids|
|Tanganjika Lake Aquarium||12-16||Tanganjika cichlids, Tanganjika catfish|
|Central America Aquarium||10-22||Guppies, Swordtails, Central American Cichlids|