Seawater desalination by reverse osmosis is widely used for drinking and utility water supply. But the formation of sparingly soluble salts in membrane devices remains a major problem, complicating the operation of reverse-osmosis (RO) membrane systems. The most effective measure to prevent the calcium carbonate and sulfate scaling of membranes is the technology of dosing inhibitors into feed water. Although a variety of effective scale inhibitors have been developed over the last two to three decades, research in this area is currently focused on the development of new types of reagents, the so-called "green" antiscalants, which do not contain phosphorus and are readily biodegradable. The use of such inhibitors does not cause eutrophication of water bodies by RO desalination concentrates discharged into them. The use of scale inhibitors has become particularly demanded in the case of desalination of seawater, since the water is alkalized and an increase in the pH sharply increases the scale deposition rate. In this study, six new phosphorus-free "green" antiscalants have been tested and compared with conventional inhibitors (Aminat-K). Experimental relationships that made it possible to determine the rate of formation of calcium carbonate in membrane devices and to compare the performance of different scale inhibitors in reducing the rates at different pH values are presented.