Magnesium: Your Magnesium is right on target. For more information consult this article.
Calcium and Alkalinity: Recommended Ranges (Levels on Target)
Before getting into problems and solutions, let’s first define what constitutes a problem and what does not. Based on published studies involving the calcification of corals and other organisms, I recommend the following:
Alkalinity (due to bicarbonate and carbonate but not borate, so those using Seachem salt must raise this value substantially to accommodate the borate being counted in standard alkalinity tests)
2.5 - 4 meq/L or 7 - 11 dKH or 125 - 200 ppm CaCO3 equivalents
380 – 450 ppm calcium ion or 950 - 1125 ppm CaCO equivalentsIf you are anywhere within these ranges for both parameters, you do not need to perform any correction on your tank chemistry, though you may choose to do so for other reasons. In this sense it makes no difference what the relationship is between the two values. If alkalinity is 4 meq/L, it is not inherently any “better” for calcium to be at 380 ppm or 450 ppm. Also, these ranges are somewhat arbitrary, especially at the high end. In fact, the primary reason for having a high end at all is that it is often difficult to keep one of these parameters above the minimum end of the range if the other is over the top end.So if one of these parameters is slightly above the high end, and the other is OK, that is not a problem worth worrying about.