Wet Processing
pH is logarithmic. Dropping from 11.5 to 10.5 costs nine times more acid than 10.5 to 10.
— L
To reach the target pH
This assumes a strong base with no buffering. Residual soda ash and silicate buffer heavily, so dose in stages against a live pH probe rather than adding the full calculated volume at once.
Fabric pH Neutralization Acid Dosing Calculator — free, with the formula and a worked example, at Textile School.