Aeration
Air pump
Useful, cheap and frequently misunderstood. The oxygen transfer happens at the water surface, so what matters is how much the rising bubbles agitate it. A pump positioned below the water line needs a check valve, or a power cut will siphon the tank onto the floor.
Short answer
A diaphragm pump feeding air through tubing to a stone or a sponge filter. It increases oxygen mainly by disturbing the surface, not by dissolving the bubbles themselves.
What it does
- Drives sponge filters
- Increases surface agitation and therefore gas exchange
- Drives air-lift devices
Strengths and where it fits
Strengths
- Cheap
- Essential backup during a heatwave or a filter failure
- Powers sponge filters in hospital and fry tanks
Good fit for
- Hospital and fry tanks
- Emergency aeration
- Sponge filter operation
- Heavily stocked tanks
Limitations and where it is the wrong choice
Limitations
- Noise and vibration
- Drives CO₂ off, which matters in an injected planted tank
- Without a check valve, a power cut can siphon water back down the airline
- Draws room air — a problem if aerosols or fumes are used nearby
Poor fit for
- CO₂-injected planted tanks during the photoperiod