An improved oxidizing composition and a method of preparing it are presented. The improved oxidizing composition includes a halogen component and a reactive core that generates a desired oxidizing product. The reactive core generates one or more preselected oxidizing products when contacted by a main solvent, and an oxidizing solution is released. The oxidizing solution contains the generated oxidizing product(s) and a free halogen from the halogen component. The oxidizing composition may be used to treat bodies of water such as pool and spa and to bleach materials. Some examples of the halogen component include calcium hypochlorite, trichloroisocyanurate, dichloroisocyanurate, lithium hypochlorite, dibromo-dimethylhydantoin, bromo-chloro-dimethylhydantoin, sodium bromide, sodium chloride, and a combination thereof.