Pumps will help oxygen to be dissolved in the water. Is this needed? If you give your fish enough living space the answer is no. How much is enough living space? Well that depends on the fish. Goldfish will require 25 square inches of surface area for each inch of fish. It is through the surface area that oxygen is added into the water and carbon dioxide is released.

In most cases you will want a pump to add oxygen to the water. Plus a stream of bubbles raising in the background is a nice addition to many aquariums.

Be warned that most pumps are noisy. It may be a good idea to ask to test the pump at your local pet store before purchasing it. If the aquarium will be in a bedroom the noise can be bothersome at night, even if it is hardly hearable during the day.

One last note. You should have an airstone at the end of your line as well. The stone is a rock with tiny holes in it. When air is pushed into the water the large bubbles are pushed though the stone and many small bubbles are formed instead of one large one. The smaller bubbles will have a greater surface area then the single large bubble when you add them all together. This allows much more oxygen to be added into the water.