Both are equally important and both should be tested.
Alkalinity is best kept withing NSW
levels 1.5 -3 mEq/l. Personally I keep mine between 2.5-3 though. As far as your current level the easiest means of reducing it is a good sized water change with aged/aerated SW
. Depending on your saltmix that should do the trick nicely. While 4.7 is on the high side, it's not at a dangerous level there's just no need for it.
As far as water chemistry is concerned, your tank (other than coralline) really has nothing in it that will deposit CaCO3
at any great rate. For now at least, water changes should maintain the necessary levels without the need for additions.
One thing that may be of concern here is having a pH of 8.0 with such a high alk
level. This can be an indication of a CO2
problem. It depends on when you tested the pH. If early in the day then there is no need for concern. If late afternoon/evening, then I would look at how the tank is set up. pH related issues are often environmental, not chemical so additions are rarely if ever the way to solve it.