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.