We propose a new method for determining the frequency characteristics of the rotational motion of an electrolyte flow during electrochemical reactions under the influence of an external magnetic field. The main advantage of the proposed method is the possibility to determine the frequency characteristics without introducing marker particles or other changes in the electrolyte or in the nature of the reaction. The effectiveness of this method is demonstrated by measuring the electrolyte rotation frequencies during the corrosion of a steel ball in an external magnetic field. It is shown that at the chosen experimental conditions the typical electrolyte rotation frequencies during etching of the steel ball are 0.88 and 1.7 Hz. The developed method can be used for determining corrosion areas of metallic compounds via in situ testing.