A saltwater aquarium requires an air pump, except for small or shallow ones. The amount of air needed per gallon for saltwater tanks is less than for freshwater tanks. Salt can corrode metal equipment if it rises to the surface of the tank. Moreover, too many bubbles can affect saltwater fish and plants negatively.  Air stones are necessary in this case because they reduce the size of air bubbles. It is important to exercise caution when it comes to how much oxygen your air pump emits. Too much oxygen on the outside of fish can lead to lumps on their bodies.