Reverse osmosis desalinating system is an advanced filtration system using TFC polyamide and acetate cellulose membranes. The membranes have very fine pores of 0.0001 micron, which allows only water molecules to pass through the filter and prevent the passage of minerals like salts ions, cations and anions such as nitrites and nitrates, metals and toxic heavy metals, organic substance and oils and microorganisms such as viruses, bacteria, algae and hogs. Membrane blockage is common in reverse osmosis desalination systems. All impurities in the water should be removed by the membrane filter. Membrane surfaces, over time, are the place for the accumulation of mineral, organic, and microorganisms, which reduces flux and recovery rates of the system and increases the pressure drop. The HydroFlow descaler make stable micron crystals consists of carbonates and calcium and magnesium sulfates in the fluid with dimensions of about 5 to 50 microns. These crystals do not attached to membrane surface, but they are excellent absorbent of other hardness ions over time and consequently the thickness of scale in membrane will reduce. The HydroFlow descaler protects membranes and increases their lifespan, increases membrane flux and reduces membrane pressure drop. HydroFlow descaler protects large scale R.O. desalination plants in 3 sections: 1- P or I series at the intake of pumps for sand filters, increase electrical flocculation and reduce polymer chemicals. 2- P or I series at the intake of micro-cartridge filters to remove biofilms and bacterial contamination 3- P or I series at inlet of the membranes to protect the membranes and deposition in the desalinizing water. The small size of the membrane input pipe is up to 11.4 inches. The S38 is recommended.