Calcium is a major constituent of calcareous algae, skeletal material of hard corals and the skeletal needles of soft/leather corals. Calcium also fulfills many biological functions. Quite often a too low calcium concentration retards coral and calcareous algae growth. NSW contains 400 – 450 mg/L calcium. Which is also the value we should strive for.

Calcium alone cannot form the skeletal material of corals and allow calcareous algae to grow.  A few other constituents are carbonate and bicarbonate. These two substances also have a major impact on the stabilization of the pH in the proper range of 8.1 – 8.4. Such stabilization is also called buffering. The total carbonate and bicarbonate concentration is also called carbonate alkalinity or carbonate hardness.  NSW has an alkalinity of approx. 2.7 meq/L or approx. 7.5 dKH when expressed as carbonate hardness. For a stable system the alkalinity or carbonate hardness should have a value similar to NSW or slightly higher and should preferably not fluctuate by more than 5%

 Magnesium is present in NSW in a fairly high concentration (1300 - 1400 mg/L). Magnesium helps maintain the correct combination of calcium concentration and alkalinity. Maintaining a correct magnesium concentration is therefore very important and is indirectly responsible for fast coral and calcareous algae growth by virtue of making the maintenance of correct calcium and alkalinity figures possible

Phosphate has several negative effects if present in a too high concentration. First of all undesirable algae growth might result. Making an aquarium an unpleasant sight. Phosphate also blocks or retards the growth of corals and calcareous algae. Scientific studies show that a phosphate concentration higher than 0.05 mg/L decreases the growth of calcareous algae by 90%!

A too high nitrate concentration can result in unwanted algae-growth and these might irritate corals in their neighborhood. Nitrate as such also retards coral growth. The nitrate concentration in a proper functioning reef aquarium should preferably be lower than 1 mg/L. Fish-only aquariums would usually show much higher nitrate concentrations. Most test kits use a procedure in which a certain part of nitrate is converted chemically into nitrite and is measured as such. Once again, just as with nitrite testing, amine interference has a major impact on the measured value. If such an interference occurs concentrations much lower than actual will be measured.