One of the most confusing aspects of keeping corals for reef keepers is alkalinity, here is a description of what it is and how the relationship works with calcium and Ph, a must read for all reef keepers with LPS or SPS corals.
''To safely avoid dangerous imbalances in the Ca-Alk dynamic, aquarists simply need to avoid pushing either component to an extreme end or both simultaneously high. Instead, think of the relationship as a Hi-Lo situation within the safe ranges. Within the accepted ranges (350-450 ppm Ca and 8-12 dKH Alk), one parameter can be pushed to a high end while the other is allowed to stray toward the middle or lower end. Any reasonably mix of the two will still provide more than enough of both elements for successful calcification'' Quote from an article by Anthony Calfo on wetwebmedia.
Entire article here.
http://www.wetwebmedia.com/calcalkmar.htm
''To safely avoid dangerous imbalances in the Ca-Alk dynamic, aquarists simply need to avoid pushing either component to an extreme end or both simultaneously high. Instead, think of the relationship as a Hi-Lo situation within the safe ranges. Within the accepted ranges (350-450 ppm Ca and 8-12 dKH Alk), one parameter can be pushed to a high end while the other is allowed to stray toward the middle or lower end. Any reasonably mix of the two will still provide more than enough of both elements for successful calcification'' Quote from an article by Anthony Calfo on wetwebmedia.
Entire article here.
http://www.wetwebmedia.com/calcalkmar.htm