THE NITROGEN CYCLE
This occurs in the same way in sea water and fresh water. In a marine aquarium
the vegetation is often less abundant than in fresh water, and so the nitrates,
the end products of the nitrogen cycle, will have a tendency to accumulate.
At high doses these pose little danger to fish but are toxic for invertebrates,
especially corals. It is therefore important to eliminate them by partial, but regular,
Once a marine tank has been put into operation, the nitrogen cycle is slower
to take effect than in a freshwater tank: around 3-4 weeks (although this is a generalization,
as every aquarium is unique).
Fish or other animals must not therefore be put into the water during this period,
although the length of time can be reduced by various means (see Assembling your
Tank, page 218), based on the principle of introducing bacteria. In any event, measuring
the nitrite levels is an excellent indicator of the progress of the nitrogen cycle.
Once the water has been put into the tank, this parameter must be measured regularly;
when the quantity of nitrites goes down close to zero, the nitrates appear and you
only need to wait a few days before inserting the fish. Nevertheless, measuring
the nitrites at regular intervals is still highly recommended, as long as the aquarium
is in use.