Here is the difference between tig/mig metal and stick welding rods. The info came from Esab's website.

This is for a regular 7018.

C 0.045 %
Mn 1.1 %
Si 0.4 %
P 0.015 %
S 0.014 %

This is for ER70s-6.

C 0.08 %
Mn 1.40 %
Si 0.80 %
P 0.010 %
S 0.001 %
Cu 0.10 %

The Mn (Manganese) and Si (Silicon) act as deoxidizers and take care of any oxygen in the weld metal.