Baking Soda is called Bicarbonate of soda or Sodium bicarbonate!
Baking Powder is the other product you mentioned with phosphate in it and there is a world of difference between the Baking Soda which I have recommended and the Baking Powder which you mentioned!!
Use the Baking Soda or the Bicarbonate of Soda or the Sodium bicarbonate, which every you want to call it, it is cheap and works!
The Baking soda provides extra Sodium in the water which may help neutralize the Excess Acids which the Epsom Salts pulls out of the body among other things, thus helping the body to Heal much faster!