Notable descaling agents include acetic acid, citric acid, glycolic acid, formic acid, lactic acid, phosphoric acid, sulfamic acid and hydrochloric acid. The calcium salts are soluble and thus washed away during dissolution or solvation. The speed of the descaling action depends on the concentration and acidity or pH of the solution provided. Hydrochloric acid is much stronger than acetic acid, for example, and therefore tends to remove scale faster. Weak acids such as acetic or citric acids may be preferred, however, where damage to the substrate is to be minimised.
Many companies offer inhibited or "buffered" acids that inhibit the corrosive effect of the acids on various materials. Approximately 10% concentrated hydrochloric acid with a corrosion inhibitor and some added penetrating and wetting agents added is typical. This allows for a better cleaning of machinery and especially heat exchangers because often the scale is mixed with silica and other contaminants.  These additives reduce the corrosion on the metals and cut through and loosen these other materials mixed with the scale for faster and more thorough cleaning.