Pat,

I hate to sound stupid (although I'm getting used to it in my old age!), but
if your pond is only 18" deep, I would think that *air* temperature is a lot
more important than the depth of the frost line?

Granted, it's been decades since I lived in PA, and then we didn't have a
pond at all -- although we had, literally, Lake Erie for a backyard!

Anne Lurie

Anne,
I was thinking that as the winter progressed and got and stayed colder that the
frost line (ie frozen ground) would get deeper and deeper. And I was hoping
that the 18" depth would be deep enough so as not to freeze the pond solid (or
close to it) If it was going to be a danger to the fishies, then I was thinking
of just bringing them in the house into an aquarium. But, it appears from what
I've read here that I should be fine with just an air pump/bubbler with a
couple of air stones submerged in the pond. Although I will keep an eye on it
and run out and get a heater if necessary.
Thanks for your thoughts,
-Pat