The pH of seawater can vary between 5.0 and 9.0. The closer the seawater is to 7.0, the more neutral the water is for sea life. If the seawater becomes acidic or alkaline, it can become uninhabitable for marine life.
Water with a pH of less than 7 is more acidic, while water with a pH of more than 7 is more alkaline, or basic. The chemical components of seawater are resistant to pH change and may remain at a more neutral level. The introduction of biological activity to the seawater and an overabundance of algae may cause the pH level of the seawater to fluctuate significantly.