What can i do if my carbon dioxide level is 18. should i be concerned?

Co2 level low: This means acidosis. 18 is not too low. It could mean kidney problem or hyperventilation. You should see a kidney doctor for a more complete evaluation.

Depends on Basis: Co2 in water is carbonic acid & is rapidly changed, under CNS control, so as to adjust blood ph. If we ventilate (breath) faster with less activity, co2 rapidly falls, ventilate more slowly with higher activity, co2 rises. Common resting, relaxed co2 ≈25 mmol/l but can change rapidly and for a variety of reasons in addition to activity and ventilation rate.