What would be the advantages and disadvantages of using tribasic sodium phosphate (aka trisodium phosphate) to soften water by removing calcium ions?
2 answers
http://hpd.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&id=3007033
For the disadvantages check the link given to you by DrBob. The main advantage is that calcium ions in solution precipitate as calcium phosphate thus removed from the water.