Watch your fish in the morning, just before the lights go on. That's when
they'll show distress, if there's not enough oxygen.

I guess I'm thinking, what happens if the power goes out at night and my
powerheads stop circulating water in pitch dark?

A power outage is trouble for a fishtank, whether it's planted or not. (Unless
you're Diana Walstead. ;-) I'd say a planted tank has an advantage over an
unplanted one.



Leigh

http://www.fortunecity.com/lavender/halloween/881/