Where does the nasty limescale come from?

Those scales are because the water is entrained Calcium sulfate CaSO4 is an insoluble substance, such as calcium bicarbonate Ca(HCO3)2, bicarbonate Mg(HCO3)2, etc., as well as multiple minerals, mainly calcium ions and magnesium ions. Calcium and magnesium are the leading causes of scale. Calcium sulfate, calcium carbonate, and magnesium carbonate are all white precipitates The shape is similar. Long-term "stirring" together becomes an annoying scale. Calcium carbonate is insoluble in water, only in acid. Therefore, making the descaling detergent neutral, it's not easy. You must try ml products!