Solutions of azo-reactive dye red 120 were treated electrochemically to study their discoloration using platinized titanium, Pt(Ti), electrodes. NaOH and NaCl electrolytes were added in the solution to increase its conductivity, change the mechanism of discoloration and hasten it and compare its efficiency to that with Na₂SO₄ additive. The active species responsible for the discoloration are formed by processes in the anode while the role of cathodic processes is marginal. It was found that NaOH changes somewhat the initial color of dye solution. The discoloration efficiency during electrolysis is small as in the case of Na₂SO₄ and Pt(Ti) electrodes and is negligible compared to that with Na₂SO₄ and Al–Pb and Ti–Ti anode–cathode electrodes. Also, a small amount of dye is coagulated/flocculated and agglomerates appear in the solution mainly on the cathode and in the three-phase interface. But with NaCl additive this efficiency is high and increases with temperature and its concentration. Discoloration occurs mainly in the bulk solution and secondarily in the attached layer in the anode. Its rate much exceeds that observed when Al–Pb, Ti–Ti and Pt(Ti)–Pt(Ti) electrodes and Na₂SO₄ additive are used. This is due to the formation of Cl₂ gas by 2D surface processes in the anode, part of which is dissolved producing HOCl and OCl^-. All together Cl₂, HOCl and OCl^- active species are more active than O^-, O^•, OH^• and O₃ formed by 3D processes within the oxide bulk in Al and Ti anodes, and much more active than the species formed by 2D surface processes with Pt(Ti) anode and Na₂SO₄. NaCl solution thus treated retains long-time discoloration efficiency, mainly due to HOCl and OCl^- contained in the treated solution. However, this efficiency is lower than that during electrolysis where the dispersed Cl₂ gas continuously feeds the liquid phase of the solution.