[mr.maroonsalty]

There is somewhere around a 25% swing in atmospheric CO2 levels in our northern climate as plants stop and start processing CO2 into sugars and O2.Yes, closed homes do build CO2 from cellular respirafion of its animal occupants, a gas range is about the only other major appliance that should change the balance of gasses as the other appliances are well vented. But there is also just not nearly the same level of O2 to dillute it as well. Back in 08 we were much more hung up on chasing pH than we were not too long after.
It seems tbat when you weigh in the advantage of the added biodiversity that maintaining well a variety of autotrophs to balancing such problems as wintertime CO2 levels, that a more balanced captive ecosystem could be reached that might in fact start asking for additional CO2 along with nitrogen.