||A novel analytical method to measure Polyhexamethylene Biguanide (PHMB) in swimming pools and spas was developed. This method utilizes nickel (II) chloride and 1,2-cyclohexanedionedioxime (nioxime) chemistry. This method will be called nickel-nioxime. Nickel ions bind and neutralize PHMB in the solution. Excess unreacted free nickel ions react with nioxime. The resulting colored solution is measured at 550 nm using visible absorbance spectrophotometry. Currently the colorimetric method to measure PHMB uses bromophenol blue (BPB). However, high levels of quaternary ammonium based algaecides and surfactant based products interfere with this colorimetric method. Currently a high pressure liquid chromatograph (HPLC) analysis is performed for samples with high levels of quaternary ammonium based algaecides or surfactants that is very time consuming and expensive. The proposed nickel-nioxime detection method achieves the same results as the HPLC method in about 5 minutes, and it is a very economical and simple method to perform.