Addition (or removal) of CO to a solution does not change its alkalinity, since the net reaction produces the same number of equivalents of positively contributing species (H) as negative contributing species ( and/or ). Adding CO to the solution lowers its pH, but does not affect alkalinity.
At all pH values:
:CO + HO ⇌  + H
Only at high (basic) pH values:
: + H ⇌  + 2 H