Airstones/Covered or Open Tanks?

Should airstones not be used in a planted tank because they drive CO2 out of
the water? Eliminate them all together?  What about covered or open tanks.
 Is it best to have a covered tank or a open tank with a pendant light?  Does
a covered tank prevent CO2 from escaping?  If you have a open tank, is there
more of a need for CO2 injection?  Any help would be appreciated.