Potassium Iodide, 5 Percent (w/v) Aqueous Solution, For Residual Chlorine, APHA - As an APHA certified solution, this item is meets the ASTM D1209 standards and can be used in water and waste water treatment facilities to determine the concentration of dissolved and particulate materials. Spectrum Chemical manufactured APHA grade products meet the toughest regulatory standards for quality and purity.