We had a good freeze last week, ended up with ice across my entire pond
except 1) where the water falls from the bio filter and 2) the skimmer.

Question is this. In order to be prepared for the next freeze (spring ain't
here yet) I'm wondering what type of heater (or bubbler) I should install.

As long as you have a hole open for gases to dissipate (sp?) You don't
need a heater.

However, if you really feel you need one, go to a farm supply and get
a floating stock tank heater.

You can order online from www.northerntools.com