Normal pH

The pH of water in the ocean is around 8.1. This is also the recommended pH of a marine aquarium, with levels slightly above or below this value considered acceptable. This happens as a result of the carbonate hardness value of sea water, which is about 125ppm. However, certain events such as biological filtration of a marine aquarium, tend to reduce the carbonate hardness value and therefore lower the pH. Also certain influences, such as carbon dioxide, can affect the reading of pH value.

Biological Filtration

The assimilation of waste by bacteria in the filter of a marine aquarium is an acidifying process and in time will reduce the carbonate hardness value of the water. As this occurs, the pH value will fall. Carbonate hardness levels can be maintained with Aquasonic Carbonate Hardness Generator Powder. At a pH of 8.1 the carbonate hardness value should be 125ppm. If the carbonate hardness value of a marine aquarium is correct, yet pH values are not, the influence of carbon dioxide should be considered.

The Effects of CO2

For pH to read correctly, carbon dioxide must be in equilibrium with the atmosphere. Carbon dioxide is produced by fish, plants, corals and bacteria assimilating waste in the biological filter in the aquarium. Some trickle (mini-reef) filters can expel carbon dioxide so efficiently that the quantity of carbon dioxide is less than the atmosphere, so pH reads higher than it really is. Likewise, in an aquarium with substrate filtration, carbon dioxide has some difficulty escaping as it is produced by the biological filter and other life. Under these conditions, carbonic acid may be formed and pH will read lower.

Using pH to Advantage

During the development of bacteria in a biological filter, ammonia and nitrate conditions ensure. Both are deadly to marine fish. The toxicity of ammonia and nitrite, however, is in direct relation to the pH value of the water in the system. By lowering the pH, the toxicity of these deadly conditions is minimised. To lessen the toxicity of nitrite, lower the pH to 7.5.