CO2 can 100% do this to your plants.... Over 4000 ppms for very long would definitely make them do what your describing.... Ive had the same exact thing happen to me.... My controller stuck in the on position...... I went into my room and it was not only hot as hell (because my burner was running constantly for hours)- but my PPMs were like 6000 when I finally got a reading..... I got the fuck outta there quick so I didnt DIE, and aired it out best I could.... The next day my plants were a funny green and all droopy looking.... People seem to think that plants cant get too much co2, but this is a huge mistake... CO2 will fuck your whole shit up if not used correctly... YOu need a good regulator/controller, and you need to check it often to make sure its running properly...