Abstract: In deinking, the flotation of fiber suspensions is performed in a cylindrical tank 2 to which the fiber suspension is fed through a coupling means 36 as primary stream. The fiber suspension is already aerated and is withdrawn through a suction connection 33 below the coupling means 36 and fed after another aeration through a secondary connection 35 above the coupling means. The volume of the circulated secondary stream is greater than the volume of the primary stream. It is thereby assured that the fiber suspension is aerated at least twice and thus better cleaned.