The pH of natural seawater varies geographically in the world’s oceans between 8.1 and 8.4. On a local scale the pH is however remarkably stable. This is due to dissolved buffers (mainly bicarbonates), which prevent pH changes. Because of the enormous volume of the ocean, a nearly inexhaustible stock of buffers are present: the sea can take up large amounts of acids, without a noticeable change in pH.

Compared to the sea the volume of a marine aquarium is very limited and therefore the alkalinity is also limited. As fish produce acid waste products and as the buffering substances are used up by calcareous algae and invertebrates, the buffer capacity may become so low that the pH could suddenly fall. This would be very dangerous to all organisms in the aquarium.

The alkalinity is measured in so called milli-equivalents of alkaline substances (for example sodium bicarbonate) per liter. These alkaline substances have the power to prevent pH drops. The alkalinity of natural seawater is approximately 2.5 milli-equivalents per liter. This level should also be maintained in the marine aquarium.

A common symptom of an unsuitable pH is pH-stress. Especially in the marine aquarium, unsuitable pH values are very stressful to fish, and increase the chance of the fish being susceptible to disease (marine white spot)

To maintain a correct and stable pH, check the pH and alkalinity weekly.

for marine water
Test Range: 7,4 - 8,6