Guide · Tubing and check valves
Air pump above or below the tank?
Why makers say to put an air pump above the water line, what back-siphoning does in an outage, and where a check valve and drip loop go if the pump sits lower.
Short answer
Above the water line is the safer place. Aquarium Co-Op says its pump should run above the water level to prevent back-siphoning, and that a check valve must be used if it sits below.[1] If your pump has to go lower, such as in a cabinet, fit a check valve in the airline outside the water, near the top of the tank, and make a drip loop in the power cord.
What goes wrong below the water line
While the pump runs, air pressure keeps water out of the airline. When it stops, for example in a power outage, water can siphon back down the line. If the pump sits lower than the water surface, gravity helps that water reach the pump and spill out around it. Danner describes its check valves as the way to stop water siphoning back into the air pump in an outage.[2]
A pump that sits in a puddle, plugged into the wall, is an electrical problem as well as a wet floor.
What the makers say
| Maker | Advice |
|---|---|
| Aquarium Co-Op | Run the pump above the aquarium water level; use a check valve if it sits below; never submerge the unit.[1] |
| Tetra (Whisper pumps) | Use a drip loop and an in-line check valve, or place the pump higher than the aquarium if that is not possible. Indoor use only.[3] |
| Tetra (CV4 check valve) | Says the valve allows an air pump to be positioned below the water level.[4] |
If the pump goes below: four steps
- Fit a check valve outside the water. Danner says its valves should go in the airline outside the water.[2]
- Put it near the top of the tank. Aquarium Co-Op recommends placing the check valve near the top so water is stopped at the rim rather than down near the pump.[5] If the valve leaks, the water stays by the tank, not inside the cabinet.
- Point it the right way. Each valve marks its direction differently; see which way a check valve goes.
- Make a drip loop. Aquarium Co-Op tells users to make a drip loop in the pump's power cable before plugging it in, so water runs off the low point of the cable instead of reaching the outlet.[6]
Check that the valve matches your tubing size. Tetra's CV4 fits 4 mm internal diameter hose,[4] while Danner's valves fit common 3/16 in inside-diameter airline.[2] The airline size guide explains the difference.
If the pump goes above
Above the water line, water has to climb back up the airline to reach the pump, so a siphon is much less likely. A shelf beside or above the tank is the simplest setup. Tetra still recommends a drip loop and check valve with Whisper pumps, and treats placing the pump higher as the alternative when you cannot fit them.[3]
Next
Questions
Can an air pump sit below the aquarium?
Yes, with a check valve. Aquarium Co-Op says its pump should run above the water level, and that a check valve must be used if it sits below; Tetra gives similar advice for Whisper pumps.[1][3]
What is back-siphoning?
Water running back down the airline into the pump, usually when the pump stops in a power outage. Danner says its check valves stop that.[2]
Where should the check valve go on the airline?
Outside the water, and Aquarium Co-Op recommends near the top of the tank so water is stopped at the rim rather than down near the pump.[5][2]
Do I still need a check valve if the pump is above the tank?
Tetra suggests placing the pump higher than the aquarium if you cannot use a drip loop and check valve. A check valve also protects the pump if it is ever moved lower.[3]
Can I put an air pump inside the cabinet?
Only with a check valve and a drip loop in the cord, and never where it can get wet. Aquarium Co-Op says the unit must never be submerged.[1]