One thing you can do for a water change is take the water from the sump. Then you put the new water in the sump. This prevents any of the fish from being spooked and prevents you from disrupting the tank.
Yup, everything through the sump. New water, additives (Iodine, Strontium, Calcium etc.) everything. That way it gets well mixed. Also I often shut off the return pump in case I mess up. Then it is isolated to the sump which is easier to correct than the whole tank.
