Chemical mechanical polishing (CMP) compositions and methods for planarizing a nickel phosphorus (NiP) substrate are described. A NiP CMP method comprises abrading a surface of the substrate with a CMP composition. The CMP composition comprises a colloidal silica abrasive suspended in an aqueous carrier having a pH of less than 2, and containing a primary oxidizing agent comprising hydrogen peroxide, a secondary oxidizing agent comprising a metal ion capable of reversible oxidation and reduction in the presence of NiP and hydrogen peroxide, a chelating agent, and glycine. The chelating agent comprises two or three carboxylic acid substituents capable of chelating to the metal ion of the secondary oxidizing agent.