Water changes provide all you need, but some salt mixes are short in some respects.
I use instant ocean. According to the myriad of tests I have performed on that mix, I come up with calcium on the short end...around 380-400 and alk at around 3.5 m.
In this case, both alk and calc will be depleted quickly. I use b-ionic in even amounts to "boost" these numbers the day after the water change, and daily to every other day depending on how much top off water at 7.6 pH I add due to evaporation.
These are the only additives i use, except for an occasional iodine (instant ocean was low on this) and magnesium, as it relates to alk-calc.
I test for everything I dose (though iodine testing is iffy at best...I dont does this unless the test reads almost non-existant levels.) Since I have been testing my mix up salt water, and my tank water before changes, then the day after, I have noticed parameters remaining very stable.