Aqua One SP150 Air Pumps are great value for money.

Features & Benefits:

Air pumps improve filtration system performance and overall water quality by increasing water flow which helps to eliminate localised build-up of toxic chemicals such as ammonia and nitrite. This makes for happy and healthy inhabitants.

The SP150 is designed for medium sized tanks.
When using an air pump, if the air pump is below the height of the water level - always use a check valve to prevent water siphoning back to the air pump.