How do I convert my existing Sodium Hydrosulfite dosage to FAS?

2026-09-17

There is no universal 1:1 conversion factor.

For example, if a mill currently uses:

8 kg Sodium Hydrosulfite / ADT

we would not recommend simply replacing it with 8 kg FAS / ADT.

Instead, conduct a dosage-response test:

Sodium Hydrosulfite:

4 → 6 → 8 → 10 kg/ADT

FAS:

2 → 3 → 5 → 7 → 10 kg/ADT

Then compare:

ISO brightness

Brightness gain

Color reduction

Brightness stability

Pulp strength

Chemical cost / ADT

This produces a much more meaningful replacement ratio.