PROBLEM TO BE SOLVED: To provide bed soil suitable for observation of fish for appreciation owing to that pH of water in a water tank for aquatic organisms of plain water shows a weak acid (for instance, pH4.0 or more and less than 7.0) region for a long term so as to hardly generate turbidity of water and algae, and enabling excellently breeding fish for appreciation, and excellently growing aquatic plants.SOLUTION: Bed soil for spreading on a bottom in a water tank for aquatic organisms of plain water comprises a silicic acid component-containing matter containing siliceous mineral, or a burned product of the silicic acid component-containing matter. The siliceous mineral has a percentage content of silicic acid (SiO) preferably of 60 mass% or more, and a percentage content of the total sum of an alkaline metal oxide and an alkali earth metal oxide preferably of 10 mass% or less.SELECTED DRAWING: None
