Water Treatment Chemicals Tetra sodium salt of 1Hydroxy ethylidene-1,1-diphosphonic acid, HEDP tetrasodium salt, HEDP.Na4/HEDP-4Na, is the sodium salt of HEDP, HEDP•Na4 is an good scale inhibitor for calcium carbonate, Corrosion Inhibition HEDP.Na4 can be used in low pressure boiler water system, circulating water system, industrial and municipal cleaning water system and swimming pool. The solid HEDP•Na4 is white powder, soluble in water, easily deliquescence, suitable for use in winter and freezing districts.