What is "calgon" ? Give structure and its uses?

Hexamer of meta phosphoric acid exist as sodium salt which is called  sodium metaphophate or sodium polymetaphosphate and it is commercially  known as "CALGON" and use as water softener.

Related Questions:

What are "pyro" oxy acids?

What are "Ortho" or "Meta" oxyacids?

What is Meta Boric Acids?

What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

What are common structural features of oxides (P4O6 and P4O5) of phosphorous?