A.R.
Mythbusters, that show on TLC, did a show about this a few days ago (or re-ran it). They found that the one that stayed the greenest and lost the fewest needles had NOTHING added to it. Just regular water. Those that had bleach, sprite, and some other odd stuff (like viagra) added did worse than the tree with nothing. You can probably find it on TLC.com if you are interested in their "research."