Also, if you are judging your CO2 tank by what the gauge says, don't bother. All that gauge is reading is the pressure inside the tank. Because CO2 is a liquid in the tank, its just reading the pressure of the CO2 gas that has accumulated above the liquid, and the gas/liquid pressure ratio is fairly constant so long as the temps don't change, meaning that the reading won't change either. Quick note, don't get worried (like I did) if you put your tank in the fridge and it looks like you've lost a bunch of CO2, lowering the temp just decreases the gas pressure.
What will happen is the gauge will stay at about the same level until you've completely depleted the liquid, at which point the gauge will quickly drop as you use up whatever air is left. If you want to figure out how much CO2 you've got you can weigh it on a scale. Somewhere on your tank there should be a tare weight and that's the weight of the empty tank. Weigh yours now, then subtract that weight and it will tell you how much of the 5lb is left. I rarely ever bother to do it though, unless I'm gonna have a bunch of people over and want to make sure I've got enough to last the night.
Edit: One other thing, on my CO2 tank I don't think its ever left the red/almost empty region of the gauge. That's just the way those gauges are setup.