BIO FILTER AND OPERATING METHOD THEREOF

An embodiment of a biofilter can include: a filter box including a discharging unit in which circulating water including fish excrement flows, and where the flowed in circulating water is discharged again; a filler that is filled in the filter box, at least a part of which is sunk into the circulating water, and wherein bacteria which turn ammonium or ammonia contained in the circulating water into nitrite or nitrate inhabit; and a siphon that controls the amount of oxygen and water supply for bacteria living in the filler by being connected to the discharging unit and discharging a portion of the circulating water through the discharging unit when the circulating water stored in the filter box reaches a certain level so as to control the volume of the fillers sunk in the circulating water.