Abstract: For detecting small level changes in an aquarium, there is proposed a sensor which, in the operable condition, comprises a substantially enclosed sensor container (18), into which aquarium water can be sucked from the surface via an overflow edge (56) and from the aquarium interior via a suction port (46) with a downstream overflow tube (52). The sucking of the water over these two paths is effected by a circulating pump (26) of the aquarium filter system via an outlet port (32) of the sensor container (18). The liquid level in the sensor container is monitored by a level sensor (64). The upper edge of the overflow tube (52) is located beneath the overflow edge of the container wall by a specified distance. If water losses from the aquarium arise, the water surface in the sensor container drops to a considerably greater extent than the water surface in the aquarium external chamber does.

Abstract: A filter for use with an aquarium is provided which is in direct fluid communication with the water of the aquarium, Only mechanical plug and socket type connections are used to connect the filter housing to a submersible centrifugal pump and to connect a closure member of the filter housing to a housing main body. No separate seal means are used. Inlet connecting means as well as outer connecting means of the filter housing are both provided in the closure member. Support means are provided to support the filter housing in such vertical position that the joint between the closure member and the housing main body of the filter housing just immerges into the water of the aquarium. Thus, the major portion of the filter housings projects above the surface of the water of the aquarium leaving a maximum of water volume accessible to fish and providing a field of view of maximum size. Thus, an extremely attractive, fail-safe and low cost filter is provided.

Abstract: The innovation relates to a centrifugal pump, more especially an aquarium centrifugal pump, comprising a motor housing containing an electric motor, and comprising a shaft tube in which a drive shaft for an impeller is arranged, and comprising an impeller housing in which the impeller runs.