Partially filled centrifuges exhibit unstable behavior over particular rotational speed ranges. To remove this unstable behavior, three different control approaches are presented which are experimentally implemented using a magnetic bearing. First, by means of a PD-controller the system stiffness is changed leading to a shift of the instability region. Second, the instability region is removed by a cross coupled feed back of the rotor vibration velocities. This cross coupling directly counteracts the fluid excitation mechanism. Third, a disturbance observer is presented which allows to estimate and compensate the not exactly known fluid force.