What to look for when buying a used CO2 tank

There is usually a hydro test date that will eventually expire. If you have an expired tank, some places charge you the $10 recert fee, some dont.

Also depends on if where you get it filled swaps tanks or fills them. Its usually the places that fill them that charge the recert fee, the trade ins usually just go in a pile with other empty ones to go back to a filling station so they dont typically charge the recert fee at those places.
 
I just went to a local welding shop and purchased mine, they just swap it out with another when you need a refill.
 
:thm: Every CO-2 tank needs to be re-inspected and re-certified at the Welding Shop/CO-2 re-fill station.
Certification is valid for "5 years" - the tank will be marked with the latest/newest certification date.
 
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