What Is the pH of Salt Water?

The pH of salt water is of concern to two kinds of people. Seamen loading cargo onto a ship take an interest in the pH level, since the higher the pH level, the saltier the water and the saltier the water, the higher the ship rides in the water and the more heavily it can be loaded. Salt water aquarium owners are also interested, since the pH levels in the salt water aquarium have a direct effect on the health of the aquarium's ecosystem.

The Meaning of "pH"

pH is an expression of concentration of hydrogen ions in a material. Water that is pure has a pH of 7. If a material's pH lower than 7, that means it is acidic. If the pH is above 7, then it is more alkaline than pure water. The pH scale ranges from 0-14.

Seawater

The pH of seawater ranges between 7.4 and 8.4 and averages about 7.6. Aqueous CO2 in seawater combines with carbonic acid (H2CO3) present in seawater, giving off a bicarbonate ion (HCO3) and a carbonate ion CO3 randomly which helps to maintain the pH level.

Salt Water Aquarium

If a pH of 7 is neutral, then a salt water aquarium should have a pH of between 7.6 and 8.4. If the salt water aquarium is recreating a reef environment, then the pH level should be between 8.0 and 8.3.

Testing the pH of the Water

To test the pH levels in your home aquarium, use the litmus paper strip that comes in aquarium test kits. The strip will have four to seven squares of a neutral color on one end. Submerge the end of the strip with the squares in the water for the length of time directed by the instructions then remove, shake the water off of the strip and compare the colors on the test strip with the colors on the instruction panel for the test. Find a matching color sequence on the strip and read the pH from the instruction panel.

Salinity and pH

While salinity is related to specific gravity, it is not the same. Salinity is the amount of mineral salts in a substance. Testing the salinity of a material requires specific laboratory equipment. The amount of mineral salts in a salt water aquarium is determined by the volume of the aquarium and the recommendation on the label of the mineral salts used to maintain the level of salinity. As the salinity increases, however, the pH of the water increases, since the mineral salts are alkaline.

Resources

• Open University Study, Relationship of CO2 to pH