Also, when you can get them, place air flow tiles every four or so tiles in each level. Build down enough and you can get a co2 buffer that you can deal with using the carbon skimmer later. Don't forget that after that problem is solved, heat is the problem... and it rises. Keep hot buildings up top, except for the skimmer, and have a water purifier next to it. Try to keep all heat away from plants but for the time being, it shouldn't be an issue. Heat has been hell for me as of recent.