I age my water (for at least 24 hours), as well as add dechlorinator to it.
Why? So it reaches room tempurature by the time I use it. That way, just in case there's a fish emergency, I have aged, dechlorinated, room temp water.
Besides, usually I just "sprinkle" the bucket of water. I don't measure the dosage per se. So, this way, I'm sure that all the chlorine has evaporated by the time I need to do a water change. (I cover the bucket with a plastic shopping bag.....otherwise, my cat will drink out of it and get cat hair in the water <img src="/images/graemlins/wink.gif" alt="" />)