Multimedia filters are used to remove colloidal materials and extraneous particles. It consists of a variety of sands, coarse anthracite over graded sand and quartz. It provides a more uniform distribution of particulate solids throughout the depth of the bed. The multimedia filter achieves a more uniform distribution of filter media throughout the bed and is considered a more effective type of filter. A typical multimedia filter for laboratory use consists of a top layer of anthracite having a 1.1-mm grain size and 1.5 specific gravity, a middle layer of sand having a 0.5-mm diameter grain size and a specific gravity of 26, and a bottom layer of garnet having a 0.2-mm grain size and 4.2 specific gravity. Normal operational flow rate is from 6 to 15 gpm/ft2 of bed area.