Disclosed herein are germicidal compositions and methods of using the germicidal compositions for disinfection and sterilization. In one aspect, a germicidal composition includes a germicidal dialdehyde and an efficacy enhancing halide salt to enhance the efficacy of the dialdehyde. One such composition may include water, phthalaldehyde, and an alkali metal halide salt to enhance the efficacy of the phthalaldehyde. In another aspect, a germicidal composition may include a carbonated germicidal solution containing dissolved phthalaldehyde. A method of forming the carbonated solution may include introducing carbon dioxide into the composition.