[Tim C]

There are many reasons why you should be careful with either the compressed air or CO2 tanks.
I chose to purchase the carbon fiber tanks new for several reasons, first, you get the most use out of the tank before re-certification is needed if you are the original purchaser.
Second, you know what kind of treatment the tank has had.
Since these tanks are used on paintball guns, the knowledge that the tank hasn't been banged around or dropped as some teenager ran around concrete barracades makes me more comfortable using it.

The info I gave here for refilling from a scuba tank was to help those engravers that live in rual areas where Paintball establishments may be hard to find, so that they can get refills for the Carbon Fiber tanks.
If you purchase a scuba tank, I would purchase it new, so that I know how that tank has been treated too.
When scuba tanks are filled, they are submerged in a tank of water while the filling process goes on.
For some reason the Carbon fiber tanks are not submerged by the local Paintball store. I don't know if there is a reason for this, or not.

I have the local store do all my filling, but if you are going to refill tanks yourself, do some research before you take that on yourself.
The store only fills my 4500 psi tank to 3,000 - 3,500 psi at the most. It is good common sense not to fill your tank to the maximum psi rating for the tank.

Since I live in South Florida, if you get stuck and can't find an answer to a question that you have about Scuba tanks. Post your question and I'll see if a local scuba shop can answer your question.

Check with the local Fire Dept., it will be a good source to get answers, they most of the time are the agency that sign off on fill station permits. Depends on the State you are in.

Good luck, hope this helps out.

Tim C