PURPOSE: A filtering apparatus for an aquarium is provided to improve a water quality purification function by changing acidified seawater to alkaline water and conveniently separate a filter within a filter by setting up a separation lid at one side of the filter. CONSTITUTION: A filtering apparatus for an aquarium which circulates and purifies the seawater of an aquarium comprises: a first filter (30) which is connected with a shutoff valve (12-2) installed at an exhaust water route pipe (11) connected to an aquarium, is formed into two stages and filters seawater to multistage in which front side is made of transparent material or translucent material； a second filter (40) which is connected with the first filter by a connecting member (13), relieves the water pressure of circulated seawater and filters the seawater； an apparatus for purifying water (50) which is connected with the second filter by a connecting member and changes filtered seawater to alkaline water； a circulation pump (60) which circulates seawater connected with the apparatus for purifying water and an air outflow pipe (61)； an air relief valve (70) which is connected with and installed at the circulation pump and exhausts air generated in the exhaust water route pipe； and a cooling device (80) which cools circulated seawater in order to flow in cooling water.본 발명은 수족관에 담수 된 해수가 일정기간이 경과하여 활어 등으로 터 발생 된 이물질을 제거하기 위하여 해수를 순환시키는데 이때 순환되는 해수는 제1여과기에서 1차로 이물질을 제거하고 제2여과기에서는 순환되는 해수의 수압을 조절하여 미세한 오염물질을 효율적으로 제거할 수 있게 하였으며 정수장치에서는 산성화 된 해수를 알칼리수로 변환시켜 수질정화기능을 향상시였으며 여과기의 일측에 배출뚜껑을 설치하여 여과기 내의 필터를 간편하게 분리수거하여 청소할 수 있게 한 수족관용 여과장치이다.
