Abstract: A method of removing iron and copper containing scale from a metal surface by contacting the scale with a composition comprising an admixture of an aminopolycarboxylic acid, such as ethylenediaminetetraacetic acid (EDTA), or the alkali metal salts or ammonium salts or amine salts of the aminopolycarboxylic acid and a phosphonic acid such as aminotrimethylenephosphonic acid (ATMP), or an alkali metal salt or amine salt or ammonium salt of the phosphonic acid. The aminopolycarboxylic acid or salt thereof and phosphonic acid of salt thereof are present in the composition in an amount sufficient to provide a molar ratio of aminopolycarboxylic acid to phosphonic acid in the range of from about 1:9 to about 39:1.