Power outages are easily one of the top reasons for total tank disasters. During a power outage, water movement comes to a halt and when that happens gas exchange will stop. Over a short time, oxygen levels in the water can become depleted, and your fish can start to suffocate. A battery powered air pump is one of the easiest and cheapest ways to promote gas exchange during a power outage. Using a simple airstone, or even just allowing a free flow of air will help agitate the surface of the water, allowing oxygen to transfer and dissolve into the water.