The invention relates to an electrolysis device for cleaning acidic waters which comprises a cathode, an anode, and an ion exchange membrane, wherein the membrane is arranged between the cathode and the anode and is attached at least along the entire circumference of its rim, wherein many inlets and outlets are arranged along the upper and lower rim of the electrolysis device which are linked to the cathode space or to the anode space, in such a way that a plug flow, ideally with a laminar profile, is created in the cathode space and in the anode space.