AMCO CLEAR TURBIDITY STANDARD, 5.0 NTU | Amco Clear turbidity standards are traceable to NIST Primary Standards on account of their consistent particle size and photometric accuracy via UV-VIS spectroscopy. Each lot is normalized to historical lots which were formulated to dilutions of ISO17034 4000 NTU Formazin. Amco Clear turbidity standards are recognized by the US EPA as a primary stnadard for the calibration of turbitidy meters online and in the laboratory for drinking water analysis. They are safe, non-toxic, no dilutions, stable, and offer a 1 year shelf life. 5.0 NTU for EPA 180.1 design instruments with 400-600 nm and 90 degree detector; such as those instruments by HF Scientific, Hach, ICM etc.