1 kg = 27.41 €
The total hardness is a value of the amount of alkaline earth metals. These metals - especially calcium and magnesium - are essential minerals and must therefore always be present in sufficient quantity in the aquarium water. In fresh water aquarium the consumption of calcium and magnesium is very low, so it is possible to enrich the total hardness only by doing a regularly water change.
The sea water aquarium, however, the calcium needs depends on the number and activity of calcifying organisms. The calcium concentration of approximately 400-450 mg/l (ppm) is perfect in sea water aquaria. Over time, the demand of calcium in the aquarium may vary.