The invention provides a chemical-mechanical polishing composition comprising (a) an abrasive comprising colloidal silica, (b) a compound of formula (I), (c) a compound of formula (II), (d) hydrogen peroxide, and (e) water, wherein the polishing composition has a pH of about 1 to about 5. The invention also provides a method of chemically-mechanically polishing a substrate, especially a nickel-phosphorous substrate, by contacting the substrate with the inventive chemical-mechanical polishing composition.