Salt deposit deterrance by Magnesium rod

[NSK8700]

I recently repaired a domestic water heater and had to replace the heater element that was heavily coated with hard water salts as well as the SS (Stainless Steel) tank had a large quantity of salt precipitate; the heater element has the option to have a magnesium rod/ element placed/ coupled with the heating elements.It is said it will deter salt deposition on the heating element. I wish someone could explain me the chemical dynamics of this.

 

[Cesium]

I think the magnesium is acting as a sacrificial anode:
http://en.wikipedia.org/wiki/Sacrificial_anode

 

[PhaseShifter]

Hard water deposits are mainly magnesium and calcium compounds. I'm guessing the surface of the Mg rod oxidizes and serves to provide seed crystals somewhere other than the heating element.

If it were serving as a sacrificial anode, it would actually increase the hardness of the water (and the amount of mineral deposits).