MG Duff Magnesium Weld On Anodes
Magnesium Weld On Anodes work better in fresh water because fresh water is much less conductive to flow of ionic current.
The higher driving voltage of Magnesium is able to deliver more current than Zinc.
Aluminum and Zinc anodes can be used in freshwater, both Aluminum and Zinc anodes bow to Magnesium anodes in freshwater.
The high current output of Magnesium is needed in the high resistivity of fresh waters.