As the weather gets colder, you may be wondering whether you need to invest in a heater to keep your goldfish warm.
I did some research into this myself, and the answer depends on what type of goldfish you have.
In general, goldfish are cold water fish that don’t require a heater. One exception is slim bodied goldfish in a pond that is at risk of completely freezing. Another is that fancy goldfish shouldn’t be kept in water that is below 50F, due to issues with blood clots.
This does not mean that goldfish don’t still require special consideration during the winter months – especially if you have them outside in a pond.
Read on, and we’ll cover everything you need to know to keep your goldfish happy and healthy this winter.
What Water Temperature is Safe for Goldfish?
Common goldfish are extremely hardy fish, and can easily survive in water that is near freezing.
In one study, scientists kept some in 39F water to study changes in their metabolism – without any harmful effects on the fish themselves.
Anecdotally, we had a fish pond in our back yard in Georgia when I was a kid, and the fish had no problems surviving in the winter, even in nights that dropped down into the teens (without a heater or anything to help them).
This is one of the reasons why I would recommend common goldfish over fancy goldfish.
Fancy goldfish, on the other hand, need a heater if the water temperature is at risk of dropping below 50F. This is because they commonly have genetic problems due to their breeding, and they can develop blood clots and fin rot at colder temperatures that common goldfish have no problems in.
This is also why I would recommend that if you live in a cold climate, keep your fancy goldfish in a tank that is large enough for them, rather than in a pond.
Do Goldfish in a Tank Need a Heater?
In general, goldfish kept in a large enough tank will not require a heater.
Goldfish are comfortable between 60-72F, which means they should be comfortable in their tank all winter long.
The exception to this would be if you keep their tank in a room that is not climate controlled or insulated – like some garages or basements. In this case, you may want to invest in a heater to make sure the water in any tank containing fancy goldfish doesn’t drop below 60F.
If you have a planted aquarium, you may want to ensure you are using a large enough air pump in the tank, as the plants will go into a semi-dormant period and will produce less oxygen than they would in warmer water.
Do Goldfish in a Pond Need a Heater?
Caring for Your Goldfish Pond in the Winter
As the water temperature starts dropping into the mid to low 50s, your fishes’ metabolism will start dropping, and they’ll start eating and digesting less food.
Therefore, you might choose to slightly overfeed them in the weeks leading up to this temperature drop in your area. Once this drop happens, though, you’ll want to drastically cut back on how much you feed them, following the below table:
| Temperature Range | Feeding |
| Above 60F | Feed normally. |
| 55-60F | Feed once per day. |
| 50-55F | Feed once per week. |
| Below 50F | Stop feeding, and remove any extra food not eaten. |
As the temperature drops, you may also want to switch to a low protein fish feed (which may be green instead of red) to help reduce waste production. This will also help with the biggest danger to your fish during the winter months.
A Critical Pre-Winter Ritual
The biggest danger lurking in your fish pond as the weather gets colder is your water quality. The cold weather provides the perfect storm that can kill your fish if you don’t put the proper measures in place to protect them.
The first thing that starts happening is that a lot of the algae in your pond will start dying off.
One reason this is important is because the decaying algae can pollute the water in two ways.
First, the algae is partly responsible for cleaning ammonia and nitrate out of the water. Without the algae, these harmful chemicals will accumulate more readily during the winter.
More importantly, the decaying algae will start releasing potentially harmful amounts of ammonia into the water all winter.
Because of this, you’ll want to clean the algae out of your pond in the fall, to prevent an ammonia spike that could harm your fish.
The other reason the algae die off is important is because algae is a huge part of what keeps your pond’s water properly oxygenated. With the algae gone, and with plants producing less oxygen in colder water, and your water could start getting dangerously low in oxygen.
Combine this with a layer of ice over your pond, and there is no real way for your pond to replenish the oxygen your fish need and get rid of the CO2 they’re leaving behind. This is a recipe for disaster in your pond.
Luckily, there are two inexpensive tools you can use to combat this: the deicer and the air pump.
The deicer is like the lite version of a pond or fish tank heater. Instead of keeping your water warm, it makes sure there is a hole in the ice, so that gas exchange between the water and the air can take place.
Put this into your pond and supplement it with an air pump (and appropriately sized air stone), and you should be able to keep your fish alive until spring with no issues.
Summary
As the weather gets colder, there is no need to worry about what sort of care your goldfish are going to need.
Any sort of goldfish indoors in a climate controlled room should be perfectly fine without any heater at all. Goldfish in a pond will require a little extra TLC, but they are still very low maintenance fish.
Just stop feeding them below 50F, clean the algae out of their pond, and provide them with an air pump to replace the oxygen the algae were producing.
Follow this simple advice, and your fish should have no problems.
