A filtering solid includes a body, the body includes at least two surfaces defined thereon, and at least one accommodating room is formed thereon. The accommodating room penetrates through the two surfaces, and at least one wall surface is formed at an interior of the accommodating room. The body is a cube or a cylinder； the accommodating room is a circular through hole or a square through hole. The filtering solid attains the purposes of reaching a maximum storage of water and increasing an adhering area of nitrifying bacteria in a limited volume.
