Thanks for taking the time to make this detailed write-up! You got a beautiful result, and I appreciate the spirit of sharing what you learned and helping people who are considering similar projects. I'm glad you measured CO2. I've recently noticed I tend to get headaches when working or sleeping in small poorly-ventilated spaces, and I'm surprised how often I encounter new structures without ventilation. I guess tig…
There isn't really any clinical evidence for CO2 levels impacting stuff beyond so called "sleep efficiency," where the effect is small (above 1000 ppm is 5% reduction in sleep efficiency) and it has the counterintuitive effect that less efficient sleep is sleeping longer, which is usually what people want. That said, placebo effects are still real.
You are wrong about the impact of moderately high CO2 levels.