Is airpump necessary?

[Neon]

plants provide oxygen only during the day not at night. As correctly said above you need something to break water surface in order to get oxygen in the water, it might be a water pump , an air pump or just a powerful filter which keeps water moving . In fact oxygen is not added by bubbles but by the action of the bubbles breaking the surface.
Now if there's no power overnight then we are in deep s..t unless you can use a battery powered air pump.

ps do you have no problems with heating ?

[bushwhacker]

if he's losing power every night filters pumps or anything electrical is not going to help..b. karthik are your tanks covered by glass? if so take the covers off it will allow better gas exchange in the tank