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.