It's going to depend on what else is in the fixer. Sometime a formula is made up from components that react to form what's needed, Rodinal uses Potassium Metabisulphte and Potassium Hydroxide to form Potassium Sulphite (and water).

So it's what the components form in equilibrium reactions in the final solution that's more important, without seening the entire list of components it's hard to be more precise.

Ian