http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
Water-softener reduces life of anode rod in gas and electric water heaters
Water heater manual says: "Artificially softened water is exceedingly corrosive because the process substitutes sodium ions for magnesium and calcium ions. The use of water softener may decrease life of water heater tank."
Six-year tanks come with 1 anode rod. Read manual.
Generally, tanks with longer warranties come with 2 anode rods.
Pick your poison now fox