The invention relates to a undergravel filter for an aquarium. The filter is disposed at the bottom of the aquarium and draws in all types of impurities, inter alia, before expelling them towards the external filter. The filter comprises: two funnels for each part of the filter such that they each form a container which directs all the matter which slips thereinto to the discharge aperture, at the base of each funnel (10). The discharge tube is triangular (11) and is located between the two funnels from which it draws in water and the impurities via the discharge aperture at the base of the funnels, on the wall of the tube. A further, wider, tube (23) draws in water and the impurities from the discharge tube and directs them towards the suction tube.
