Here's my two cents. I'd consider 10% water changes per week. So a five gallon bucket will work for a mixing container. I'd put 3 gallons of RO/DI water in this bucket. I'd also use an old powerhead to get the water mixing. Add your salt like you're salting a big batch of french fries. That is, don't just dump it in as a clump. You'll be using somewhere in the area of 1 1/2 to 2 cups of salt, dependent on the salt you're using. At this point, the water is room temperature, that is, no heat. It's counterintuitive, but new salt mixes better at cooler temperatures. Once the salt is dissolved (I like to let it sit overnight), throw a heater in there and heat it up to your tank temperature. Now is when you use ideally a refractometer to measure the salt content. Add more water or salt as needed by your refractometer reading. You can not do this when the water is cool....you'll get a higher number when cool compared to when it's heated up. Once you've matched salinity and temperature, siphon out three gallons and pump/dump the new water into the DT.....done!
