In an aquarium, aeration stimulates the flow of oxygen by releasing air bubbles into the water, thus creating water movement. Filtration is the use of different devices to draw debris out of the water, thus keeping the aquarium clean and stimulating water movement to a lesser degree.
Approximately 50% of all common aquarium diseases are caused by stress and dirty water. Better water movement will force the debris into the filter, thus making the tank water cleaner. Oxygen combined with clean water will create healthier living conditions for fish.
There is no such thing as too much filtration or aeration. By combining the two, you are increasing the odds of having active fish and a disease free aquarium.
Freshwater Aquarium Filtration