Good article and this was what I was looking for and my primitive chemistry mind then assumes higher magnesium within limits other organisms can survive would reduce the ability of calcium precipitation at higher pH. I thinkMagnesium bible;
Aquarium Chemistry: Magnesium In Reef Aquaria
This article details the nature of magnesium in seawater, how it is added, measured, and removed from marine aquaria, and how it impacts the maintenance of calcium and alkalinity.reefs.com
“More interestingly, the magnesium levels were found to have a very large impact on the rate of precipitation. In batches with no magnesium, and at natural calcium and elevated carbonate levels, calcium carbonate was found to precipitate in minutes. With a natural seawater level of magnesium added to that mix, the precipitation was delayed to 13 to 20 hours. With double the natural magnesium concentration, the precipitation was delayed to 22 to 29 hours.”