When the hardening-forming cations calcium and magnesium are replaced by sodium ions, this is called SOFTENING. The strong acidic cation exchanger used in this process is called a softener and can then be regenerated again with sodium chloride. SOFTENING is used, for example, in standard household dishwashers to prevent unsightly chalk stains on dishes. So always refill with dishwasher salt so that the softener in it works reliably!