Fish tanks are a way to bring the beauty and serenity of the natural world indoors. Outside of the tanked environment, the natural movement of water in lakes, rivers and oceans provides aeration that the fish need to survive. In a tank, that aeration and oxygenation must come from a pump, which circulates air into the water, allowing it to bubble out and oxygenate the water. A fish tank pump is fairly simple and inexpensive to operate, and when it stops working, you will need to troubleshoot the cause to learn whether the pump needs to be replaced. There are a number of simple steps to take to determine why your fish tank pump is not working.
Check the electrical socket that the pump is plugged into. If you are using a ground fault outlet, unplug the pump, press its reset button and plug it in again to see if it operates. If you are not using a ground fault outlet, plug a lamp into the outlet and see if the light comes on when you turn it on. Try plugging the pump into a different outlet in your home or office as well, to see if it works there. If not, check the circuit breaker for the outlet at your breaker panel. If everything is operational, you have a problem with your pump, and you will need to troubleshoot further.
Check the pump tubing. If the pump is functioning but no air is coming out into the water, check your air line tubing for kinks and blockages. Since most air line tubing is clear, this is fairly easy to do. You might even remove your air line tubing, clean it off, and blow through it with your mouth or compressed air to see if you can move air through it manually. If you cannot, replace the air line tubing. If you can move air through the tubing by means other than the pump, your problem is likely inside the pump.
Check the pump diaphragm. The aquarium air pumps are simple diaphragm pumps that have a rubber cup inside that is moved by a small motor. The movement of these diaphragms sucks air in, and a one-way valve forces the air out into the air line tubing. If the pump diaphragm is cracked, broken or leaking, or if the diaphragm has hardened and does not move, the diaphragm will need to be replaced before you can continue testing the pump. If the motor is not operating, the pump will need to be replaced.