Kewl, thanks for the quick answers!
BTW I do make sure to keep non-breathers off those worlds, and I'm glad to hear that the AC should work for my other people. My population is humungous at this point, as I have about 6 jam-packed huge breathables (plus a few large/med/small breathables) in only 4 systems. It's freaky when you're doing a cargo swap and all of a sudden your population is 7000 out of 500 o_0 so I make it a point to avoid that.