Mixing Saltwater and getting it back into your tank....

[The Guy]

I mix ro water and the salt in a 25 gallon barrel I have, you can use a power head or whatever you have to mix it. I usually put a 150 watt heater in with it while it's mixing. After it's well mixed at the temp. you want add it to your system. My tank is 90g with a 50 g sump so I figure I have approx. 100 gallons of water when you figure the rock displacement and the fact the sump is running half full.
I shut off my return pump, then suction out of all but a couple of inches water and detris I can, then all my new water goes into the sump. Been doing it this way since set up as advised by friends that were already into reefing. Seems to work well with no ill effects. Maybe others can chime in on how they do water changes.