WATER, A HAVEN FOR LIFE

water, carbonate hardness (CH) is used in sea water, where it serves to measure the
quantity of calcium and magnesium carbonates and bicarbonates present. This is crucial for maintaining the pH, and for growing corals, which have skeletons made of calcium carbonate.

PH VALUES
As sea water is salty, its pH is therefore higher than that of fresh water. Pure sea
water in the middle of the ocean has a pH of 8.3- Near the coasts, this drops to about
8 or a little less, as its dilution with fresh water lowers the salt content. The pH of
sea water in an aquarium must vary between 8 and 8.5; beyond these values,
animals will experience certain physiological problems.
Variations in pH in a marine aquarium Sea water contains a great deal of calcium carbonate
and bicarbonate, and there are only slight variations in pH in a natural setting.
It is a different matter in an aquarium, a restricted habitat operating as a closed
cycle. The pH must not fall below 8, but a slow and regular decrease in this parameter
may be seen. Why? The water in an aquarium sometimes contains too much
carbon dioxide, which has a tendency to lower the pH.
What can you do? The first step is to measure the CH:  if it is under 7.2°CH, add calcium or
replace some of the water. This situation is, however, fairly rare in an aquarium without
corals, solely occupied by fish; if it is over 7.2°CH, there is an excess of
carbon dioxide. Stirring of the water must therefore be increased by using diffusers or
an electric pump.

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,
water changes.