im doing 2000 as well. the people at the grow store arent always right and some times absolutely wrong. when i asked them about co2 they told me to run it at night! they also said my air cooling wouldnt work on my lights but it is hard to keep my temperature up now that they are air cooled. all plants need co2, whether one or a hundred and it will make fatter nugs and speed harvest time. check out my nugs at two weeks into flowering. thanks for the props. peace