paintball tank as a fill tank

Yes, most paintball tanks are regulated down to a final output of 900-1800 psi (so I'm told). My local paintball guy said he could order me a Ninja carbon tank, rated to 4500 nominal pressure, and with an output pressure of 3000 psi. This at a cost of 150 bucks. It's a small tank, so I would only use it in the field, or to top off after filling the gun first with my scuba tank.
My scuba tank requires a visual inspection every year, with a hydro every five years. I'm not certain if the standards are so high for tanks that are not used for "breathing air" (which most paintball shops do NOT have the expensive filtration system for). A paintball tank, using "unclean" air, may not require inspection as often due to it not being used for breathing (major health/safety issues when using "unclean/unfiltered" air vs. the air a scuba shop fills with...for your lungs, not for the gun!). Hope this is helpful, best of luck!

if you have a tank already you can just buy the ninja reg with an output of 3000psi and screw it on. just to let you know its not hard.