Here's a bit more information about Calgon and 20 Mule Team Borax (Previously posted):
Super Washing Soda, White King & 20 Mule Team Borax: Precipitating water conditioners, they bind the minerals in the wash water but minterals can redeposit if not rinsed out really well. Can cause minerals to build up on fabric and the inside of your washer. They can also be irritating to skin if not rinsed very well.
Calgon: Calgon is a non-precipitating water conditioner and binds the minerals into a solution that does not redeposit on clothing or the inside of the washer. It must be added to both the wash water and the rinse water for highest effectiveness. It is more gentle to clothing and skin. It is also more expensive to use.
I pre-mixed White King powder in water bottles, when liquid Calgon was not available, to add to my holding tanks. The powder solidified into solid crystals that completely filled the bottles and could not be removed. I did not want that mixture in my holding tanks.