| 摘要 |
PROBLEM TO BE SOLVED: To obtain the sand of a water tank for rearing an organism to be reared in the sea water, consisting mainly of a carbonate mineral, having the amount of thermal weight reduction caused by a decarbonization reaction in a prescribed range, having a property for controlling an alkali degree and an electric conduction degree suitable for the rearing of the organism, having a water quality-maintaining function, and easy in the maintenance control. SOLUTION: This sand contains 23-56% (converted into CaO) of calcium and 0.01-35% (converted into SiO2 ) of silicon, and the amount of thermal weight reduction mainly caused by the decarbonization of a carbonate salt mineral is 18-44%. Or, the sand contains 0.1-5.0% (converted into CaO) of calcium, 70-97% (converted into SiO2 ) of silicon, 0.0-10.0% (converted into Al2 O3 ) of aluminum, and 0.0-4.0% (converted into Fe2 O3 ) of iron. The sand has a thermal weight reduction amount of 0.01-7.0%, wherein the thermal weight reduction is mainly caused by the decarbonization of a carbonate salt mineral. When the sand is soaked in distilled water, the rise in the electric conduction degree of the sand is 5-35μS. The whole alkali degree and phenolphthalein alkali degree of the sand are 30-45mg/liter and 1.5-5.0mg/liter, respectively. In the particle size distribution of the sand, the sand having sizes of 0.2-7mm occupies preferably 60-100%.
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