The calcium and magnesium salts dissolved in the water
The total hardness, or generald hardness, shows the calcium and magnesium salts dissolved in the water. There is no general advice for an optimum value. Most species like medium hard water (8 – 12 °dGH). East African ornamental fish, however, live in hard water with about 15 – 30 °dGH.
To reduce the hardness, we recommend AQUAVITAL BLACK PEAT or AQUAVITAL GRANU-PEAT. To increase the hardness, place stone or gravel containing calcium (e. g. coral sand or marble stone) in the water.