Any reason not to use tanks before viz?

[kelemvor]

As long as you check them for oxygen % and CO you're good. Which you should be doing every single time you dive them regardless of needing a vis

It's a good idea but nobody checks o2 content until they get into nitrox. Very few of us also check for CO. Personally, that's exactly what I'd do, but I doubt someone diving air has the necessary equipment to do it.

 

[AfterDark]

Unless the tank has been sitting for 30 years with moisture in it the O2 % is fine. O2 doesn't disappear but it can be used up if oxidation is going on inside the tanks.