I have had to keep tanks alive in the event of poweroutage by using a gallon pitcher and repeatedly scooping and pouring the water. The more exposure to o2 you can get the better. I poured it from about a foot above the tank and tried to cause as much agitation as possible. I have also used a bank of rv batteries hooked up to a power-inverter to run airstones in my tanks to keep oxygen up( charging them back up everyday with a truck and jumpercables, it would take about an hour and a half at 1500rpm). I have also heard of pouring hydrogen peroxide in tanks as it is h2o2 and when exposed to the tanks water releases an oxygen molecule and turns into highly oxygenated water.