If I were you, I'd start off by making dead sure your refractometer is calibrated. Then, go ahead and run your full panel test for macros and nutrients.
Macros
Cal
Alk
Mag (least consumed)
Nutrients
Nitrate
Phosphate
Test your macros daily over the course if 5-7 days and then average your consumption.
(Example)
Monday calcium is @ 440 tuesday 420 wednesday 395 and so on....
You would see the decline in
#s, add the differences up and divide them by the number of days you tested for to get your 5-7 day average consumption of that element.
Then, mix your 5 gallons of salt water, do a 5 gallon water change and measure parameters after it fully mixes in your tank.
This will tell you how much a 5 gallon water change is making your values swing.
For stability. Your numbers shouldnt differ too much day to day...when they do....that means your tank is unstable. This will help stabilize it among other things and help you keep coral long term based on parameters alone.
Nutrients can be pushed out to testing every week. These can be balanced with water changes and routine maintenance....filters and such. Some people even need to dose nutrients depending how their tank is set up and whats inside