Hach-Lange ULTRATURB sc basic_plus_seawater - Manual (Page 25)

Maintenance
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The turbidity of this parent solution is 400, stated in Formazine Attenuation Units
(FAU) or Formazine Nephelometric Units (FNU). This solution can be stored in a
dark place at 25 °C (±3 °C) (77 °F (± 5.4 °F)) for around 4 weeks.
Formazine reference solution
Dilute the parent solution with the aid of pipettes and measuring flasks to produce
reference solutions in the required range. These solutions can only be stored for a
very limited period.