Like Dr. Marco, I'm a bit more lazy -
I mix with RO water from Wal-Mart or Publix (using Red Sea Coral Pro salt - mixes with great parameters), stir it up, then drop in a powerhead for a day or so. I don't heat it because usually the temperature in our apartment is within a couple degrees of the tank water.
We have a strange system - I remove three or so gallons from my 25 gallon reef, then replace with new water. The three gallons from the 25 go into the 40 gallon kind-of-reef-with-a-leopard-puffer tank, usually along with another 3 gallons of new water. Then, some of the water removed from the 40 are put into the 10 gallon random-tank-with-some-rock-and-hermit-crabs-from-the-Keys tank, which desperately needs a good cleaning right now :mrgreen:
Seems to work out okay, since the water I remove from the 25 is usually a-ok as far as parameters go, anyway.