The HANNA® turbidity calibration solutions are produced according to the AMCO AEPA-1 standards, at 0, 10, 20 and 500 FTU. They are preferred to the formazine based standards, as they are non-toxic, stable, reusable and long-lasting. They are preferred to the formazine based standards, as they are non-toxic, stable, reusable and long-lasting. Order Information: AMCO-EPA solution @ 0 FTU (30 mL)