A chemical indicator element for use in an aquatic environment water parameter testing system. The chemical indicator element includes a chemical indicator and a thin film material having particular optical characteristics tied to the light from a light source, such as a light source of an optical reader element of a water parameter testing system. The chemical indicator element may also include at least one of a backing material that absorbs one or more wavelengths of the light of the light source and a holder including a material that absorbs one or more wavelengths of the light of the light source.