If you go to an organized field, most of them won't let you use a scuba tank because a) they want you to use their air and b) liability of someone possibly using a tank that is currently out of certification.
If you just go and play with friends in the woods and such, they are handy to have so you can always get some extra air. Just be aware that most scuba tanks that paintballers by are aluminum 80 cubic ft tanks, which are only pressurized to 3000 psi, so they can only fill your tank that much. You also would need the fill adapter to fill your pb tank. Lastly, like paintball tanks, scuba tanks need to be visually inspected and hydro tested. The hydro test last 5 years. The visual lasts only one year and is certified by a sticker with the month and year of the visual. You will need to have both of these current to get the scuba tank filled at a store. Most paintball stores do not fill scuba tanks, so you will most likely need to find either a scuba shop or a sporting goods store that has a scuba department to fill it. Some scuba shops, however, will only fill tanks for certified divers, not for paintball.
One last note, if you look around for used scuba tanks, be sure that any aluminum tanks you are thinking about getting have a made date with a year of 1989 or newer.
Pm me if you have any specific questions on regards to the specifics of scuba tanks.
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