During blackouts or power outages it may get to a critical point where the fish in your tank are running low on oxygen. You can provide oxygen to sustain them by manually supplying air into the water. An effective way to do this is by sticking a straw into the tank and blowing air through it. Avoid inhaling through the straw to keep from sucking fish into it and to keep from getting tank water in your mouth or from swallowing any debris from the tank like fish feces. Blow into the straw for several minutes and take a short minute or two break. It’s important to keep replenishing the oxygen especially in dire situations where the fish are close to dying.
This is also an important technique if when the electricity comes back on your tank doesn’t start. You can help to keep the fish alive until you get the fish pump started.
Blowing up a balloon and emptying the air into the tank can provide quick bursts of oxygen. It may be able to put an increased amount of temporary air into the tank giving you more time to work with a pump that has stopped depending on the size of the balloon. Aim the balloon lip away from the fish and control the flow of the air by squeezing the lip. If the air is let out in a single rapid burst from the balloon it can spill water or even knock fish out of the tank.
Disinfect and rinse the balloon lip and neck thoroughly, if you are going to reuse the balloon, before putting it back into your mouth.
An eyedropper can be used to squeeze oxygen into a tank. Place the eyedropper below the surface. Squeeze the air into the tank and resurface. Take the eyedropper out of the water and give it a squeeze then let it go allowing it to take in air as the dropper bubble expands before submerging the eyedropper back under the water and squeezing to release the air. An eyedropper may be too small to make a difference but there are other bigger eyedroppers out there than what is used on the eyes. There are larger versions of eyedroppers like those that are used to baste things, sometimes in their own juices, when cooking. Sometimes larger eyedroppers come in enemas. Use a clean eyedropper and always make sure to disinfect and rinse it if you are going to save it to use again.