Department of Transportation (DOT) requires cylinders (bottles) to be tested regularly. The Hydro Date is the month and year the bottle was safety tested. Paintball cylinders need to be retested for its serviceability every three to five years. They also only have a lifespan of 15 years...
Your tank needs to be hydro-tested in the month prior to its born on month. For example, a tank that had been hydro-tested in November of 2017 should be tested again in 2022 because its certification is up in December...
Hydro testing for paintball and scuba tanks / bottles with HydroLabWA in Bremerton, WA