Sugar doesn't filter out THC to my knowledge. You can use any bong liquid as long as it does not contain alcohol, lipids (fat), or any other solvents.

Crystal light has artificial sweeteners, not sure which because I don't drink it, but prolly splenda or sucralose or aspartame, etc. These are nasty, bad, man-made chemicals that are proven carcinogens in many animals- these companies claim they have not been shown to cause cancer in humans, but that is merely due to the fact that no humans have volunteered to have these chems tested on them under lab conditions.

peace