I have obtained an experimental setup of a Marx bank which has electrolytic liquid resistors. In the tubing of the resistors are various strength solutions of copper sulfate. I was told that the electrodes are copper but there appears to be some sort of plating or other reaction occurring. This leads me to believe that the electrodes are not pure copper. Air bubbles are forming from what I presume is this reaction as there are no apparent leaks. There also is some sort of sludge forming around the electrodes and is also settling in the lower parts of the tubing due to gravity. Does anyone have any kind of advice on how I could determine what reaction is actually occurring here? Or does anyone have any insight on what other possible reactions could be occurring besides electrolytic plating? The liquid resistors were replaced and we made sure that there were no air bubbles within each tube prior to installation. Current was run through the tubes to ensure they had the correct resistance. Most of the larger electrodes have pitting occurring as you can see in one of the attached photos.