Would Bubling Oxygen Through "Dead Zones" Like A Fish-Tank Make Much Difference?
Actually, if you could get the oxygen in there, you would probably turn the dead zone into a "feast zone," because all that algae would be food.  But I think it would be prohibitively expensive.  Fish tanks aren't deep, so it doesn't take much pressure to force air bubbles into the bottom.  And they're not large in volume, so you don't need huge amounts of air bubbling.  Oceans, or even rivers or harbors, would be another matter.
Also, some of the algal blooms are poisonous "red tides."