Sodium carbonate is Na2CO3 and sodium bicarbonate is NaHCO3. In other words, both are salts of the carbonate ion (CO3)2-, but in one it is bound to two sodium ions Na+ and in the other one sodium ion and one proton H+.
If you are adding the salt to increase carbonate hardness, there is no difference between the two. If you are adding it to raise pH, carbonate will have a stronger effect than bicarbonate. Remember that low pH indicates a high concentration of protons H+, and you are adding some with the bicarbonate. If you dissolve the salts in pure water, sodium carbonate you will give you a pH of 10.6, sodium carbonate will lead to a pH of 8.3.
Just googling the terms, I found a wonderful article about the carbonate system, that I can warmly recommend if you want more details.
Frank
If you are adding the salt to increase carbonate hardness, there is no difference between the two. If you are adding it to raise pH, carbonate will have a stronger effect than bicarbonate. Remember that low pH indicates a high concentration of protons H+, and you are adding some with the bicarbonate. If you dissolve the salts in pure water, sodium carbonate you will give you a pH of 10.6, sodium carbonate will lead to a pH of 8.3.
Just googling the terms, I found a wonderful article about the carbonate system, that I can warmly recommend if you want more details.
Frank
