Rusty, The Co2 pushes all the O2 out through 3 small breather hols at the top of the dome. I don't think I am overdosing them as they are very green. I do not monitor the levels and I dose them 2 or 3 times a day. the constant pressure from the air pump pushing the co2 out with it should only have the biosphere charged for no more then 3 hours before getting replace by oxygen.
Co2 aids in the process of photosynthesis and as we all know that's how they make energy to give us the honey. so anything that has a great potential to help I will try. BTW the girls are not as yellow now and are as green as grass. pun intended. I am not keeping it constant. Just a boost every few hours during lights on. clones show no sign of wilt on day 3 in rockwool in biosphere.