My Powertig 250 ex manual states only pure argon or argon helium mix. No co2. My I mig 250 states 75/25 for steel. No pure Argon for steel with the Mig. Does this also mean that pure argon for the Tig for steel would be wrong? I plan on purchasing pure argon to weld aluminum with both machines. However I am hoping I don't need to buy 75/25 for the Mig and argon/helium mix for the Tig to weld steel. That would be 3 different gases and I'm trying to save money and only use two gases if possible. All help appreciated!