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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 hinders coral and calcareous algae growth.


Magnesium is present in NSW in a fairly high concentration (1300 – 1400 mg/L). Magnesium is an essential part of chlorophyll, which is necessary for photosynthesis. Without photosynthesis plants, including algae and the corals, which we usually have in our aquariums, would not be able to live. Magnesium has another important function since in fact makes maintaining the correct combination of calcium concentration and alkalinity or carbonate hardness possible.


Ammonia and ammonium are substances which should be converted rapidly into nitrite followed by nitrate and nitrogen gas. If this does not happen then the aquarium is not fully cycled or biological processes are not proceeding as they should.

Nitrite Testing

Nitrite is a substance that is toxic to fish and invertebrates. It is a misconception that once a tank is through its cycle (first 3 or 4 weeks) that nitrite has vanished. Many nitrite test kits suffer from interference by amines (such as naturally occurring and essential amino acids) resulting in a too low measured value especially if the nitrite concentration is relatively low.

Nitrite is converted to nitrate in properly cycled aquariums. The thus formed nitrate is transformed into harmless nitrogen gas (=denitrification). This happens in areas deprived of oxygen within live rock and miscellaneous filter materials. Before it can be transformed to nitrogen gas the nitrate is first converted back to nitrite. When for whatever reason this particular cycle can not be completed, toxic nitrite can be present in significant concentration and readily be detected by test kits that do not suffer from amine interference.

 Alkalinity Testing

Calcium alone cannot form the skeletal material of corals and allow calcareous algae to grow. Some other substances are needed as well. 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. The only difference between alkalinity and carbonate hardness is a conversion factor.