Abstract: A filter apparatus for use with an aquarium tank comprises a filter housing with opposite front and rear walls and opposite end walls and a bottom wall defining an open topped construction. A hanger means is for suspending the filter housing in coplanar relationship with one of the aquarium tank walls. A J-shaped hanger clip defines a long leg extendable into the tank interior and a short leg extendable into the filter housing interior. Bolting is engageable through the short leg for bringing the wall of the tank and confronting wall of the filter housing into tightenable clamping position relative to each other. In the filter housing is an upper seat for upwardly supporting a splash box having an apertured bottom wall for water drainage and a filter compartment therebelow filled with a biological fiber wool for the filtering of the water charged thereinto and a return hose and complementary motorized pump for the return of the filtered water from the filter housing to the aquarium tank.