Most of us know the basic process, (all though I do use a powerhead to mix water, and I do so for 24 hours). But the reasoning behind keeping the parameters unchanged was really interesting. Also I think its time to buy a salinity refractometer.
http://www.reefland.com/forum/saltwater-fish-only-aquariums/22147-how-make-successful-water-change.html#post159585
http://www.reefland.com/forum/saltwater-fish-only-aquariums/22147-how-make-successful-water-change.html#post159585