Guide · Air pumps and aeration
Air pump flow explained
How to read an air pump's L/min or L/h figure, why depth changes real output, and why 'for 40 gallons' is a maker suggestion, not a measurement.
Short answer
Air pump flow is published in liters per minute (L/min) or liters per hour (L/h); multiply L/min by 60 to get L/h. Makers rarely say at what depth they measured, and output drops with depth, so a published figure is a ceiling, not what you will see at the bottom of your tank. A label like "for tanks up to 40 gallons" is the maker's suggestion, not a measurement.
Two units, one conversion
Some makers quote liters per minute, others liters per hour. Put them on the same unit before you compare:
| Pump (maker figure) | As published | Converted |
|---|---|---|
| Tetra Whisper 10 | 0.5 L/min[1] | 30 L/h |
| Tetra Whisper 100 (outlets joined with a T) | 3.3 L/min[1] | 198 L/h |
| Aquarium Co-Op single-outlet | 1.1 L/min[2] | 66 L/h |
| Aquarium Co-Op dual-outlet | 1.6 L/min[2] | 96 L/h |
| Fluval A101 (one outlet) | 90-110 L/h[3] | about 1.5-1.8 L/min |
| Fluval A202 (two outlets, total) | 180-220 L/h[3] | 3-3.7 L/min |
Tetra publishes 0.5, 1, 1.3, 2.6 and 3.3 L/min for the Whisper 10, 20, 40, 60 and 100, and marks the 60 and 100 figures as measured with the two outlets combined by a T.[1] Fluval's A202 figure is also a total from two outlets.[3] When a dual pump's flow is split across two air stones, each one gets part of it.
These are all maker figures. None of these pages says what depth or method was used, so the table puts them on one unit; it does not rank the pumps.
Depth changes real output
An air pump has to push air down against the weight of the water above the outlet. The deeper the air stone, the harder that is, and the less air comes out. That resistance is backpressure.
The two independent measurements we found both measured flow by timing how long a pump took to push out one liter of water:
- FishLab says it tested over 60 pumps, timing flow through airline at 10, 20 and 30 inches of depth with adjustable pumps at maximum.[4] It reports that depth affected both air output and noise, especially for pumps made for small tanks.[4]
- ModestFish measured five dual-outlet pumps with an inverted bottle, averaging two runs, but does not state a test depth.[5]
Because the methods differ, their numbers cannot be merged into one ranking. Cite each as "FishLab measured" or "ModestFish measured", and compare pumps only within one publisher's results.
Some makers state a depth limit instead. Tetra says Whisper pumps can be used in tanks up to 8 feet deep,[1] and EHEIM gives its air100 a maximum pumping head of about 2 m.[6] A depth limit says the pump still works there, not how much air it moves there.
"For 40 gallons" is a suggestion
Tank-size labels are the maker's suggested tank size. Tetra offers the Whisper line for aquariums from 10 to 100 gallons, and those gallon figures are suggestions, not measured flow.[1] Fluval suggests the A202 for aquariums up to 80 US gallons (300 L),[3] and 50 and 160 US gallons for the A101 and A402.[3]
A tank-size label cannot account for your depth, the number of air stones, or what else moves the water. Use it to shortlist, then check the flow figure and whether each outlet has its own control. Fluval, for example, says each A Series outlet has its own flow control dial.[3]
Check the voltage before the flow
Some well-documented pumps are sold only for 230-240 V, 50 Hz mains. Sicce lists its AIRLIGHT 1000, 1500 and 3300 at 60, 90 and 200 L/h, all rated 230-240 V / 50 Hz,[7] and EHEIM lists the air100 at 100 L/h with 50 Hz ratings only.[6] Neither is a North American 120 V / 60 Hz product, whatever its flow. The 120 V vs 230 V guide explains how to read the label.
How to use the numbers
- Convert every figure to the same unit.
- Note whether a dual pump's figure is per outlet or a total.
- Expect less than the published figure at the bottom of a deep tank.
- Treat tank-size labels as a maker suggestion.
- Confirm the 120 V / 60 Hz variant before anything else.
Next
Questions
How do I convert L/min to L/h?
Multiply by 60. Tetra's 0.5 L/min for the Whisper 10 is 30 L/h; Fluval's 90-110 L/h for the A101 is about 1.5-1.8 L/min.[1][3]
Does a deeper tank reduce air pump output?
FishLab reports that tank depth affected both air output and noise in its own measurements, especially for pumps made for small tanks.[4]
What does 'for tanks up to 40 gallons' mean on an air pump?
It is the maker's suggested tank size. Tetra, for example, offers Whisper pumps for 10 to 100 gallon tanks, but those labels are suggestions, not measured flow.[1]
Can I compare flow numbers from two different makers?
Only roughly. Makers rarely state the depth or method behind a flow figure, so treat two makers' numbers as a starting point, not a ranking.
Is more airflow always better?
No. More flow means more bubbles and usually more noise; match the pump to what it drives, such as one air stone or a sponge filter, and use the outlet's flow control if it has one.