It helps to have the water airated, use a power head. I've never used a heater because my room temp is same as tank temp, most of the time. In summer, it's higher, so I add a little at a time. Check the levels of the water before adding it to the main tank. Make sure sg, ph, ect are the same. If you have a lot of money in your tank, or want to be extra careful, test the other stuff (alk, calc, ect) with each new bag/box of salt you use.
I've figured out it helps to keep water mixed on hand. Just keep a covered bin or bucket somewhere, with a ph in it.