A method for predictive maintenance for a magneto-inductive flow-measuring device and/or to a method for determining electrical conductivity of a medium flowing through a magneto-inductive flow-measuring device, wherein the magneto-inductive flow-measuring device includes a magnet system, which produces a magnetic field passing through the measuring tube essentially transversely to a measuring tube axis; at least two measuring electrodes coupled with the medium, having a defined rest potential and being arranged in a region of the measuring tube lying essentially perpendicularly to the magnetic field; and a control/evaluation unit, which delivers information concerning volume- or mass-flow of the medium on the basis of measurement voltage induced in the measuring electrodes. A first exciting signal with a first frequency (f1) and at least a second exciting signal with a second frequency (f2), or an exciting signal containing at least two frequencies (f1, f2) are/is applied to the measuring electrode in such a manner that the average value of the exciting signals or exciting signal coincides, at least approximately, with the average value of the electrode potential of the measuring electrode. On the basis of at least one impedance value measured between measuring electrode and reference potential, conductivity of the medium and/or change on the surface of the measuring electrode are/is detected.