The quiet, powerful Tetratec APS Aquarium Air Pumps are available in 5 different models - for aquaria up to 600 Litres. The airflow of the can be easily be regulated via the air-tap, which is included. Oxygen is essential for the health of fish, plants, and filter bacteria. Water contains far less oxygen than air, and so oxygen levels can quickly become critical in aquariums. New TetraTec APS air pumps offer an easy way to increase oxygen levels, by pumping air directly into the aquarium, therefore ensuring that oxygen requirements are met. In addition, many aquarium ornaments are air-driven, and require an air pump to operate them. Undergravel filters also require air pumps to run them. TetraTec APS air pumps are suitable for all these applications. Designed in conjunction with leading sound engineers, TetraTec APS pumps are unrivalled for delivering high air flows with the minimum possible sound. The different models are as follows:- APS 50 for aquariums containing 10 -60 Litres APS 100 for aquariums containing 50 -100 Litres APS 150 for aquariums containing 80 -150 Litres APS 300 for aquariums containing 120 -300 Litres APS 400 for aquariums containing 250 -600 Litres Please Note image show is of a APS 300 - packaging may vary between models.