There is provided an additive and method for removal of calcium from crude oil or its blends containing calcium naphthenate at low pH as well as at high pH varying from 5 to 11, preferably from 6 to 11, more preferably from 7 to 11, wherein the additive is glyoxal and said pH is of the wash water for crude oil processing systems.There is also provided an additive and method for removal of calcium from crude oil or its blends containing calcium naphthenate, wherein crude oil is treated with wash water containing alkaline medium selected from the group comprising sodium hydroxide (NaOH or caustic), ammonia or amine compound, or mixture thereof, and wherein pH of the wash water or of the processing mixture in the desalter varies from 5 to 11, preferably from 6 to 11, preferably from 7 to 11, characterized in that the additive is glyoxal and the crude oil or its blend is treated with glyoxal.