Ah ok. So basicallly you have 3 things here, each needing their own test kit. Red sea calcium and alk is not a typical 2-part, so they are not dosed evenly. All of these are dosed based upon daily consumption with the exception of magnesium that can be dose much more sparingly (drains slower).
The way to find daily consumption is to test one day, test the next day at the same time (without dosing), and dosed what was consumed. Keep testing daily for a week so you get a good idea as to how your tank is consuming alkalinity and calcium. Magnesium likely won't be drained fast enough for this to work, so simply test it once and then again after 2 or more weeks. I used to dose magnesium once a month when I used their product line. Alk drains fastest, followed by calcium, and then a massive lag behind in 3rd for magnesium. Add alk to an area of high flow, slowly, and preferably away from corals as it can "burn" them. You should space out the dosing of each to not be at the same time. If you dose them all at once, they will precipitate (basically combining on the spot due to super high concentration in that spot). Alk should not be raised more than about 1KH at a time (it boosts the pH dramatically). Calcium and magnesium can be added in large quantities without issue.