Can a paintball CO2 tank run on compressed air?

Yes, most sear tripping (mechanical, tippmann style) paintball guns, however, will run, with some fine right tuning, on either CO2 or compressed air. Most blowbacks (tippmann, spyder, azodin, bt) are "meant" to run on C02 and may run into problems with HPA without some internal adjustment. With very few exceptions (SP1 and SP vibe) spool vavle markers cannot run on CO2, and those that can, need an anti siphon tank so they do not get liquid into their valve. Almost every other gun will run great on HPA.