For most beginner gardens and growrooms, ambient CO2 levels are sufficient. (I know you're an experienced gardener, so this is for the benefit of others considering this technique)

If you have the experience to recognize plant ailments, they'll let you know how they feel about the situation. But if you're a beginner...try and bring a grow or two to harvest before you try and overclock the plants. For me, there's not enough benefits in CO2 use to justify a complete failure or two that can set you back for months. Especially if you need the meds asap.
(learn to walk before you try to run)

Am curious...why do you feel you need the CO2?
How long does the CO2 hang-around in the dome, and how are you keeping your levels consistent? (you realize that without air circulation the CO2 will settle at the roots, right?)
How are you monitoring the CO2 levels so as not to overdose 'em?