Calcium

• The skeleton of corals is primarily composed of calcium carbonate. They usually get the calcium from surrounding waters. Depletion of calcium, especially if the calcium level falls below 360 ppm, can cause stunted growth. Good aquarists maintain the calcium levels between 380 and 450 ppm, the levels present under natural conditions.
  
  

Alkalinity

• Alkalinity is another important factor to consider when growing corals in an aquarium. Under natural conditions, corals take bicarbonate from water and convert it to carbonate, which is used to produce the corals' exoskeleton. Hence, measuring the presence of bicarbonate in the water will give a good idea about how alkaline the water is. Ideal alkalinity for salt water aquarium housing the corals should be between 2.5 and 4 meq/L. For quick alkalinity corrections, you can use baking or washing soda.
  
  

Salinity

• Salinity in an aquarium can be measured using conductivity probes, refractometers and hydrometers. It is advisable to keep salinity at natural levels, which is 35 ppt.
  
  

Temperature

• Maintain the aquarium temperature between 80 and 81 degrees Fahrenheit throughout the year. Metabolic rate increases with temperature, and this results in an increase in consumption of use more oxygen, carbon dioxide, nutrients and calcium. While higher temperatures can stimulate growth, it also increases waste production. Also, at higher temperatures, the solubility of oxygen in the water is adversely affected.
  
  

pH

• It is important to monitor an aquarium's pH level. Each marine organism needs a specific pH range. The ocean's normal pH is around 8.0 to 8.3. The rate of formation of exoskeleton decreases as pH level falls. Generally, there is no consensus on the ideal pH for corals in saltwater aquariums, and hence, it varies from one tank to the next. According to Reef Keeping website, a pH range of 7.8 to 8.5 is acceptable, provided the alkalinity is maintained at 2.5 meq/L and calcium levels in the water are about 400 ppm.
  
  

Magnesium

• Magnesium in a saltwater aquarium has an effect on calcium and alkalinity. Magnesium tends to increase the amount of calcium carbonate in the water by binding to the surface of the carbonate. However, when magnesium is low in the water, the nonbiological calcium carbonate levels increase in the water and hence, calcium and alkalinity levels cannot be maintained. Keeping the magnesium levels of 1285 ppm is preferred, but a range from 1200 to 1400 is also acceptable.
  
  

Phosphate

• Phosphate levels are typically low in natural conditions. In an aquarium, phosphate enters the water through the food fed to the corals. If phosphate levels increase, it will prevent calcification of the corals' exoskeleton and stunt their growth. Also, it can cause algae growth to increase in the tank. It is advisable to maintain phosphate levels below 0.03 ppm.
  
  

Ammonia

• Ammonia levels of even 0.1 to 0.2 ppm are harmful to fish, phytoplankton and other marine organisms, including corals. Ammonia is produced by the organisms living in the water. It is advisable to maintain at near zero by using ammonia suppressants.