In order to keep your reef tank at optimum parameters for coral growth in terms of your Calcium, Magnesium and KH levels there are many methods but in our opinion the easiest way to do it is by dosing.
Dosing can be done by using a two part or three part method. Two part being something like Seachem Fusion 1 and 2 and three part being RedSea A,B and C as an example.
Both of these methods consist of the major elements; Calcium, Magnesium and KH, however, in two part, Fusion 1 would be your Calcium buffer and Fusion 2 being your KH buffer. Both in turn help maintain Magnesium levels as there is just the right amount of Magnesium in the two part to help with maintaining your Magnesium at its optimum range.
Three part is all three of these major elements in their individual components and you would dose them according to your uptake of each as well as a bit of a buffer to last throughout the day till your next dosing interval.
Using a dosing unit would be preferable for both of these methods as you are able to spread your daily dose out across the 24 hours in a day or you can dose your daily dose in one go. Either way works just as well as the other. However, having a spread out dose limits the possibility of fluctuations between dosing intervals.
Our recommended range of Element levels:
Calcium - 450ppm
Magnesium - 1350ppm
KH - 9-10.5 dKH
These are the levels we keep our reef tanks at and from our experience, we yielded the best results at these parameters.
Testing your parameters is important in order for you to know how much of each you will need to dose.