An apparatus for automatically purifying a fish tank. The apparatus comprises a physical filtration area (3), a biochemical filtration area (7) and a water trapping area (2). A water inlet of the physical filtration area (3) is connected to a fish tank. The physical filtration area is provided with two water outlets, with one water outlet being connected to a sewage discharge gate (4), and the other water outlet being connected to one water inlet of the biochemical filtration area (7). The other water inlet of the biochemical filtration area (7) is connected to a water outlet of the water trapping area (2). A unique water outlet of the biochemical filtration area (7) is connected to the fish tank (1). A water inlet of the water trapping area (2) is connected to an external water source. The physical filtration area (3) is internally provided with a water distributor, filter cotton (9), a pulsator rotating mechanism, a sensor (13), a sewage discharge valve (4), a heating rod, a sterilizing lamp and a circulating water pump (5). The water distributor is connected to the water inlet of the physical filtration area (3), is arranged above the filter cotton (9), and is used for spraying raw water onto the filter cotton (9) for physical filtration. After being subjected to physical filtration, the raw water is heated by the heating rod, is sterilized by the sterilizing lamp, is pumped by the circulating water pump (5) into the biochemical filtration area (7) for filtration, and then returns to the fish tank (1). The filter cotton (9) is arranged on the pulsator rotating mechanism and can rotate therewith to automatically clean the filter cotton (9).L'invention concerne un appareil permettant de purifier automatiquement un aquarium. L'appareil comprend une zone de filtration physique (3), une zone de filtration biochimique (7) et une zone de piégeage d'eau (2). Une entrée d'eau de la zone de filtration physique (3) est reliée à un aquarium. La zone de filtration physique es
