By the way, this is a real issue. WHen my STUPID DC RETURN PUMP died, I came home and found my fish lethargic with two of them lying sideways on the ground, even though I have two Vortech MP-40s on the tank, neither was high up enough to really move the surface of the water... that was mostly by design as those pumps can really start a ... vortex and such air downwards, so I leave them deep. Anyway, I immediately grabbed a small powerhead that had an air-line venturi on it, and ran it in the tank so it created a LOT of bubbles. Soon most of the fish actually looked better ... except for my Klein Butterfly, who was already dead by that point.
As a backup (which I've not done yet) I'm considering adding a HOB filter (with no media in it) to the back of the tank to provide surface agitation OR adding a powerhead in the tank WITH an air venturi, but with the venturi set to just below the surface so that it sucks in water normally, but will suck in air if the return pump fails and the display tank water level drops. Neither of these will work if the power cuts out, but will save the fish if the return pump dies. If the power goes out, the B-11 air pumps will kick in.
As an aside, I find it "funny" that my brand new expensive fancy DC pump would die so easily, but my cheapo Via-Aqua 2600, which has been running 24/7 for almost 20 years is still going strong as my return pump, with only a short break where it was replaced by the treacherous DC pump.
V