I don't know if an aquarium heater will be able to do the job depending on how cold it gets in your part of PA. It also would depend on how large your pond is. I use a bubbler and some people use a heater designed to keep just a hole open (as opposed to trying to keep the pond warm).

Why does the size of the pond matter if all I'm looking for is a small hole in the ice?

A larger body of water is capable of absorbing more heat than a small one. Additionally the fish tank heater is only expected to have to raise a few gallons by a few degrees, your home heater does most of the work. IIRC a 50 Watt heater is only recommended for something like a 35 gallon tank anyway (inside!). It is going to quickly burn out. There are lots of reasonable pond heaters in the 300 Watt range, getting the right thing now is better than having to panic in mid January.

Do you think a bubbler would be a better idea?

I don't know what kind of winters you see in PA so I can't say for sure but at least where I am (Zone 5) the inexpensive bubblers can fail if it gets extremely cold (the cheap pump diaphragms freeze and crack). I used to run both but the only reliable choice here was the heater (though I never tried a good compressor style air pump).

Floating water deicers aren't that expensive. I forget what brand mine is, but it did the job well last year. And last year was a nasty winter.

Thank you

You didn't say what size pond you have. I agree that the aquarium heater won't keep up. I have a 300 gallon in-ground stocktank and use a 1250 watt deicer. It comes on below 40 degrees F. Sometimes it seems like too much, and frogs seem to come out of hibernation..........but if it's really, really cold, icy and snowy, it barely keeps a hole in it.

I have another suggestion. Would a powerhead from a fish aquarium work? this device circulates water for under gravel filter's in a fish aquarium. The volume is pretty strong, I was thinking that this would circulate the water in a small area enough to keep it from freezing. My pond is 4 feet deep and is approximately 4000 gallons. My heater broke last year and froze over, I am trying to use something other than a heater with just circulation. Thank you for your thoughts.

I really think you'll find that any device designed to work in an indoor aquarium will fail when used outdoors. The temperature extremes are hard on anything electronic or electrical in nature unless they are specifically designed for that purpose. That's just my opinion though. I guess you won't know unless you try, but I would definitely have a back up plan in place.

I bought a de-icer for a horse trough for about $15 at a local mill store. Worked like a charm in my 750G pond all through this past brutal winter.