Sounds like a bad idea. If you were to accidently close it, or it were to get back upped up, you would have an awful mess on your hands. I had air valves on mine, but only isolate bottles during mixture changes. I think trying to adjust the bps count on a DIY system is not really feasable. It is going to change constantly anyway as the mixture ages, and then you change the mixture.
Your best bet is to use 2 bottles, stagger the mixture changes, and experiment to find what mix recipe / time frame gets you the most consistent bubble count for your tank.
