This is a cut and past from the faq
A variation is to spray seltzer water on the plants twice a day. This is not recommended by some authorities, and receives great raves by people who seem to feel it has enhanced their crop. It stands to reason this would work for only a small unvented closet, but may be right for some situations. It could get expensive with a lot of plants to spray. Use seltzer, not club soda, since it contains less sodium that could clog the plants stomata. Wash your plants with straight water after 2 or 3 seltzer sprays. It is a lot of work, and you can not automate it, but maybe that is good! Remember, being with the plants is a beautiful experience, and brings you closer to your spiritual self and the earth. Seltzer is available at most grocery stores. Club soda will work if seltzer water is not available; but it has twice as much sodium in it. A very diluted solution of Miracle Grow can be sprayed on the plant at the same time. One factor of using selzter water is it raises humidity levels. Make sure your venting humidity during the dark cycle, or you could risk fungus and increased internode length.
I use a sodium free seltzer I got from wally world which allows me to not worry about the sodium build up.....
I hope this helps ya decide what ya do..