A method of controlling the pH of a print reaction zone in an electrolytic matrix printer is described. Appropriate amounts of a buffering agent are included in the treated surface layer of the recording medium used in the printer to hold the pH of the print reaction zone in the range of 5.0 to 7.0 and, preferably, between 6.0 and 6.5. The pH of the electrolytic reaction zone can also be held in the desired range by adding appropriate amounts of a buffering agent to a supply of recording medium moistening fluid, either before and/or during actual printing, the latter step enabling dynamic buffering control if needed. The described method halts or reduces the degradation of print electrodes by effecting a balance between excess quantities of acid or base material generated in the print reaction zone during printing.