Question about CO2 tank

Got a hailer half keg kegerator off Facebook marketplace got a full co2 tank and just a cheap 1/76th keg to test it out and figure out how it’s supposed to work, ive noticed the co2 tank has drained to nearly empty after about a week of being connected to the keg, regulator set to ~12 psi, is this normal? Potentially related been getting super foamy pours and some bubbles in the beer line