You've probably already guessed it: If there are anion exchangers, there must also be CATION EXCHANGERS! As the name suggests, the resin of a cation exchanger attracts the positively charged ions, i.e. cations, from the water and exchanges them with others. During softening the water, calcium ions can be replaced by sodium ions, for example. If a CATION EXCHANGER is oversaturated, it can be regenerated using acids or salts.