2-3 out of 1 tank?!?!?!

you must have some serious leakage then, I can get about 7-8 weeks out of 1 tank. and Im doing over 30 rats a week.

Are you constantly running the air into the tank?

I just turn it on for about 4 seconds then turn it off. The CO2 is heaveir than air, so it will sink to the bottom.