Should I change my current cylinder of 75/25 to straight Argon for TIG welding?

Only been welding for about two years and it has been MIG with 75/25. Self taught which is scary. Decided to get into TIG since I think I could make nicer welds on the small hobby and yard ornaments I make. Just got the Everlast Power i-TIG 201 this week because of the HF start feature and automatic gas control. Beautiful piece of work and I did managed to get it fired up this weekend. Current tank is 75/25 on my MIG welder. Ran 15cf to my TIG and actually got to get it working a bit. Noticed that most of the things are laid a bead on started looking rusty in a matter of minutes. I assume this was oxidation from the CO2. Considering picking up a 125CF bottle of 100% Argon just for the i-TIG since I still have close to a full large tank of the 75/25. Am I right about the oxidation and should I start using straight Argon immediately (buy a new tank) or wait till my current tank gets replaced? Appreciate your help.

Yes! For TIG you need pure Argon.

Thanks for confirming this. Think I'll run down a buy a cylinder tomorrow and just finish my large tank of 75/25 on the MIG.

It's scary how many people call me telling me something is wrong with the welder. Happened twice this past week at least. After going through all the techniques, and possibilities of settings, they often add that they've changed gas as well and their 75/25 mix isn't contaminated because they already checked that.:O And overlooking the fact there is a big "No CO2" picture on the connections page.