Is Goldfish hard to keep in a backyard pond?

They are quite easy and prosper in the great out doors.

Winter is another thing you have a couple of choices leave them in the pond and put a floating heater that keeps the pond from freezing solid. You could set up a tub in the basement or garage with a small pump.

you do not feed them after the temp fall below 50 degrees so there is not mess.
point in fact this cool down and heat up is a spawning trigger.
 
It depends on where you are, and how deep your pond is. My pond is about 5' x 7', and 29" at it's deepest. If you have cold winters, your pond should be at least 2' deep, preferably 3'. I live in New England where the surface freezes over each winter. You will need a pump and filter to clean and aerate the pond year-round, and if it's cold in the winter, a floating de-icer. If the surface of the pond freezes over, the trapped gases beneath will kill your fish. My pump does bubble at the surface of the water, but it still froze over a few times last winter a few times, so that de-icer saved my fish. You will also need to regularly feed your fish in the warmer months, the occasional insect or plants aren't enough. Once the temps fall below around 50 degrees, they cannot properly digest food.

There are several kinds of goldfish that are hardy, such as Comets, Shubunkins, and Sarasas. They need about 40-50 gallons of water per fish. They grow to about 12" in length. Koi are harder to keep, they grow as large as 36", and need at least 1000 per koi. They are also very messy, and need a good filtration system.
 
You don't necessarily need a heater to keep a hole in the ice, water movement will do the trick as well. I keep my waterfall running all winter and it keeps plenty of movement for gas exchange. I also don't bring my fish in over the winter, they stay outside and when it warms up in the spring they start breeding. I think I fed my pond fish half a dozen times or so last year. Once the pond is established, there are plenty of insects, plants, algae and other microorganisms to support the fish. If you want them to grow faster, by all means feed them every day. I'm just in no rush to have 2-3' koi in my pond.
 
my brother had his smallish pond in his backyard for 8 years...never put a heater in and never ran any type of filter or pump...and never had a goldfish die. Guess he got lucky?
 
Nah, that's pretty common. Goldfish are amazingly hardy and adaptable; they have established populations in nearly ever major body of freshwater in North America from at least the Great Lakes to Texas, and probably further north and south. They can survive remarkably well in hypoxic conditions; I've seen ponds thaw in the spring with dozens of dead frogs in them, but the goldfish were all fine.

This doesn't mean you shouldn't provide an opening in the ice for them, just that iceing over doesn't always kill them. This is especially important in areas where the ice on a pond is likely to last for weeks or months, rather than just days.
 
Yeah, our ice gets 6" thick or more. I don't have a waterfall, and the pump fountain at the surface does freeze over. And if you have a really small pond, there are less insects etc. for the fish to eat, so I would feed them. That's why I originally stated it all depends on your location and the size of your pond. If someone were to put a tiny, shallow, preformed plastic pond in the ground in the colder northern states, with no aeration or heater, they'd have fishcicles come spring. And in the warmer months they might be able to survive without food, but it wouldn't mean they were healthy. JMO
 
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