Calcium is a major constituent of coralline algae, the skeletal material of hard corals and the skeletal needles of soft/leather corals. In many cases too low a calcium concentration retards coral and coralline algae growth.
Magnesium is present in natural sea water in a fairly high concentration (1350 - 1500 mg/L) and is an essential element of chlorophyll which is necessary for photosynthesis. Without photosynthesis plants, algae and coral would not be able to survive.
Strontium plays an important role in accelerating the growth of calcareous algae (coralines) and corals. Natural seawater contains approx. 7-9 mg / L of strontium. As the growth of corals and calcareous algae goes hand in hand with strontium and calcium depletion, depletion of calcium usually means strontium depletion.
Calcium is not the only substance needed to form the skeletal material of corals and allow calcareous algae to grow. Carbonate and bicarbonate are also needed and these two substances can have a major effect on stabilizing or buffering pH levels in the aquarium in the correct range of 8.1 to 8.4.
The pH value in a marine tank has a major impact on the growth of corals and calcareous algae and on many biological processes. The pH should not be allowed to fluctuate more than approx. 0.2 units during any 24 hour period and should preferably be kept above 8.2.
Nitrates (NO3) are the result of nitrite (NO2) degradation by denitrifying bacteria. Nitrates are assimilated by algae, so you do not want to have too much algae in your reef / marine aquarium, you must work to limit the concentration of nitrates (NO3).
Nitrites (NO2) are among the most harmful dissolved compounds, they are extremely toxic. Nitrite (NO2) should never be present in the water of your aquarium except when it is started. But at no time should the animals in your aquarium be exposed to nitrites.