Only 1/2 psi a day? Are we talking about thin 700x 20 to 28c sized tubes? I use on average 100 gram tubes and for the last 40 years or so I average about a pound to two pounds a day depending on the thickness of the tube and the manufacture, maybe heavier 130 plus gram tubes would lose 1/2 psi a day, I know my touring bike that uses a 35 to 45c tube loses about a pound a week, not sure what the weight of those are. Of course latex tubes lose a lot more at around 30 psi a day if I remember correctly.