[1_T_Submariner]

I have had a tank for 3-4 months and used it with no problem. Not sure how air would go bad. It couldn't get contaminated if the tanks where full that I know of anyway. I'll check back and see what others say.

Now let me address the other problem. Did you buy 6 tanks then not take them diving? If I lived closer I would offer to excersize them for you.

Edit:
Steel or Aluminum? Sizes?