Hi Brooothru,
Keep in mind that, in water, 1mg/L ~= 1ppm. So, 1 mg of NaMeta in 1L of water yields ~.24 ppm sodium, whereas 100 Mg of NaMeta in 1L of water yields ~24 ppm sodium.
To get there, the NaMeta (SMB) molecular formula is Na2S2O5
The Elemental/Atomic masses of constituent elements...