This paper (the fourth in a series) reports the results of a theoretical and experimental study of the decalcification of seawater on different ion-exchange sorbents by simultaneous use of electroselectivity reversal and ion-exchange isothermal supersaturation MUSS) effects. A detailed evaluation of the influence of the sorbent properties on the efficiency of the IXISS-based self-sustaining seawater decalcification process was carried out through a series of computer experiments using a mathematical model of the dynamics of ion exchange. It was found that the best sorbent to be used in the process is a modified A-type zeolite. The modification of the zeolite includes sequential treatment of the initial ion exchanger with dilute magnesium-containing solution (or seawater) and concentrated sodium salt solution. The first treatment was carried out at elevated temperature [15-20 degreesC higher than the temperature at which the modified zeolite (MZ) is expected to be used, T-ex],and the second was performed at T-ex. The complete regeneration of the MZ after the calcium sorption cycle was carried out with the calcium-free brine produced by the seawater desalination unit. The process is continuous and operates in the closed-cycle mode.