You need to track several aquarium water parameters for a healthy reef tank. The pH should be 8.0-8.4, kept alkaline using a crushed coral (aragonite) substrate. The salt concentration (specific gravity) needs to be at 1.023-1.025. An alkalinity of 9-11dGH will keep the pH and hardness stable. Calcium levels of 400-500 ppm and magnesium levels of 1200-1350 ppm are also important for proper skeletal construction.