How long will oxygen last in the water? I have a 20g nuvo that had only 2 clowns in it and 3 frags. Tank is not new and has been cycled for over a year. Fish were qt long ago with copper power/prozi/ and focus products. Last night we lost power at 7pm I grabbed my deep cycle boat battery and hooked it up to a inverter and ran just the return pump From 7pm to 8am when I left for work. Before I left the battery measured 11.92v I thought it would be ok until I got home or had my mom come over and check on them. She come over at 2pm to put my food in a cooler since power was still not on and when she got there the pump was off because the inverter didn't have enough power. Right then the power come back on and I had her plug the return pump back Into my eb8. She said the fish were acting weird so she face timed me and In the vid they looked normal. When I got home at 7pm they were dead. I'm assuming it was lack of oxygen. I tried my best with what I had. I don't know exactly when the pump shut off at so my question is how long could they last with no water flow? When my apex connected water was only at 80 degrees so it wasn't a temp issue. I'm just ticked at myself cuz I did my best with what I had and I was 3 hrs away for work and couldn't get home. Salinity/temp/ammonia all good I'm guessing its just lack of oxygen.