To pose this differently: if my calcium levels are lower, but they don't decrease in a week, is it necessary to raise them? Is this purely a situation for usage, or does the existence of a higher calcium level (even if not decreasing) is beneficial?
The truth is no one knows exactly what correct lvls of mag, calcium or alk are to have in a home aquarium, some aim for natural sea water lvls some aim higher, it’s a case of picking a range and keeping your lvls within that range and hope it works for your tank.
With AFR you are meant to only start using it when your lvls are where you want them, AFR will then try and keep them there, each tank has different corals etc so it can only add the average amount of elements that the average tank uses, you keep alk as stable as possible and the AFR will add in enough calcium and mag to keep the lvls correct, calcium is easier to balance as it normally follows alk, mag can be a little different as it is not so easy to predict, but you will only see your mag creep up or down over weeks or months not day by day.
Once alk is stable calcium should not increase or decrease, but worth checking monthly to see where it’s at, you can then add a little calcium to get it back to where it needs to be, or stop AFR for a small time to lower it, you would then add a separate alk to keep alk stable whilst not dosing AFR, but AFR is very good at keeping lvls balance so changes tend to be small and not very often. Same with mag, as said mag will be slow to see the change generally so no need to test often.
The aim is to see your lvls in the same range every time you test, not trending up or down.
Here is a good read to set your lvls. Once set it’s good to use a salt within those lvls so you don’t have to keep altering them with water changes. (Small water changes would not alter the lvls much, only large changes).
