Too cold for bubblers?

I live in Central PA - current temp - 5 degrees F - nighttime temps are
below zero.

My question is, I have a *raised* pond made of cinderblock (was here when we
moved in) and the single goldfish that was here when we moved in survived
the winter last year just fine w/out any "assistance" - the pond was already
frozen when we moved in, so we were delighted when we saw him alive and well
in the spring.

We added some friends (I've posted here in the past about that) and for the
winter, I bought bubbler stones - two long ones - which were working pretty
well until this really cold snap. My concern is that the water surrounding
the bubblers will freeze and burn up the pump (which is a cheap small one,
but works well) - and my worst fear is it'll catch on fire or something -
since I have the pump inside the house (figuring the warm house air going
into the bubblers wouldn't be a bad thing).

So, my question is, should I unplug it altogether until warmer weather or
just let it keep going? The pond looks frozen solid and the pump doesn't
*sound* much louder than it did......but I'm still concerned. I thought of
adding a de-icer, but I have no idea if that would really help or not -
we're talking about a 10' x 10' (roughly) water area that's 18" deep. Am I
being overly-concerned about the fish since the one *did* survive w/out
anything last year?

Thanks,
Nicole