How carbon dioxide influences the pH value
When you fill the whirlpool with water, heat it up and swirl it, the carbon dioxide is released. Carbon dioxide dissolved in water is an acid. When it is outgassed, the water becomes more alkaline. The pH of the water rises. Because carbon dioxide is missing as a "calcium solvent", the water-soluble calcium ions are converted into limestone.
The rising pH value indicates that the carbonic acid is outgassing. The faster the carbonic acid outgases and the higher the pH value rises, the faster and stronger limestone can form.
To prevent the formation of limestone, an acid is usually added to the water. A pH reducer or also called pH minus. This acid takes over the function of the carbon dioxide and leaves the calcium in dissolved form in the water. Therefore the control and lowering of the pH value is a very important factor to avoid limestone formation.Deshalb ist die Kontrolle und das Senken des pH-Wertes ein sehr wichtiger Faktor um eine Kalksteinbildung zu vermeiden.
The connection between water hardness and carbonic acid also explains why the pH value behaves differently with soft water than with hard water. With soft water it can be that you only have to lower the pH value for two to three days and it then remains stable. It remains stable as soon as the carbon dioxide is outgassed. With hard water it can be that the pH value must be permanently lowered for weeks. It rises again and again. With hard water you also need much more pH reducers than with soft water.