Calgon (a water softener) is:

Calgon is sodium hexa meta phosphate $\left({\mathrm{Na}}_6{\left({\mathrm{PO}}_3\right)}_6\text{ or }{\mathrm{Na}}_6{\mathrm{P}}_6{\mathrm{O}}_{18}\right)$

Hard water is softened using calgon. When Calgon is added to hard water, the sodium ions from the anion of Calgon are replaced by the calcium and magnesium ions of the hard water. In the form of a combination with Calgon, this causes the removal of calcium and magnesium ions from hard water. As sodium ions are released into the water, the water is softened