[Newt]

No Salt - it is not needed and can harm some plants and fish species.
No carbon is needed either.

 

[Newt]

Carbon will remove a lot of elements needed in the tank that the plants use.
If you have a well balanced tank then you only need carbon to remove any meds you might need to use.
A well balanced tank will not have a bad odor.
Carbon also has phosphate that will leach out even if the manufacturer claims no phosphates.
I've had my current 75 gal set up for 8 years and have never used carbon.