Based on the Ksp experiment, what is a way to "soften" water by removing calcium ions?

Answer 1

I recommend using tribasic sodium phosphate, also called trisodium phosphate, TSP. a colorless water-soluble compound, Na3PO4•12H2O, occurring as crystals: This can be purchased at the Chemistry Store http://www.chemistrystore.com/trisodium_phosphate.htm
for less than $2/lb

The phosphate ion is excellent for removing calcium ions from water since the Ksp value for calcium phosphate Ca3(PO4)2 is a very small 1x10-26 which means most all of the calcium ions will be removed upon the addition of the phosphate ions.