AMCO Clear is an EPA approved primary standard for calibration of turbidity sensors that is safe, non-toxic and disposable. It is easy-to-use with no dilution or resuspension, and it is available in a wide range of values. It is NIST traceable to particle size/distribution and optical density, and its inherent stability means it does not settle from suspension. It has a guaranteed one year shelf life even if you've opened the bottle and happened not to have recapped it tightly. The convenient submicron polymer suspensions are non-toxic primary calibration standards approved by the US EPA for drinking water analysis for turbidity. AMCO Clear is the unique, non-toxic low-level turbidity standard that can reliably read from 0.02 NTU to 10,000 NTU every time.