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Can Fish Survive Without a Heater.Let’s Find Out!

6 min read

A fish tank heater is a common piece of equipment in most aquariums. It is required if you have tropical fish such as bettas and/or live in colder climates.

After all, it is important to keep your fish – which are cold-blooded creatures – warm and comfortable.

Betta  fish in a fish tank

As with any device, an aquarium heater may fail to do its job sometimes. Maybe it is a power outage. Maybe it is the heater itself that has become faulty. Either way, it could be dangerous for your fish – you don’t want to come back and find your fish frozen to death right?

So how long can fish survive without a heater? The answer will let you figure out how much time you have before disaster strikes. In this article, we will also look at how to heat an aquarium without a heater and how long a fish tank heater takes to heat up.

Let’s get started!

How Long Can Fish Survive Without a Heater? It Depends on Various Factors.

If you are looking for a simple answer, you won’t find one. There are a lot of factors that determine how long your fish can survive without a heater, such as the following.

Fish Type

Certain fish like warm water, while others like cold water. If you are using an aquarium heater you probably have tropical fish, which requires a water temperature between 75° to 80° F.

When the temperature drops below 60°F, tropical fish will suffer. However, other fish may not mind it that much – they can tolerate lower temperatures for a longer time.

Tank Size 

A larger fish tank can retain heat much longer than a smaller one – it’s simple physics.

The mass of water you have determines how much heat it holds; more heat means it takes more time for the heat to dissipate to the surroundings, so you have more time before the temperature drops to room temperature.

It can be explained in terms of the specific heat capacity, which reveals how much energy is required to increase( or decrease) a unit of mass by one degree. 

Water has a specific heat capacity of 4182 J/kg °C. Relatively speaking, that is quite high, which is why your aquarium will take a while to reach room temperature.

That means you shouldn’t worry too much with a 50-gallon tank. A 5-gallon tank is another story, however.

Room Temperature

Time for another physics lesson. You may have learned that the rate of heat loss is directly proportional to the difference in temperature.

That means if the ambient temperature is really low compared to the tank temperature, the latter will drop really fast.

Room temperature is usually around 68-72 °F, but it may vary depending on weather and your thermostat setting.

Tank Insulation

Insulation can prevent heat loss. How insulated your tank is determines how fast it will lose temperature.

Usually, fish tanks will be made up of glass or acrylic – both good insulators.

You should also consider whether your tank is open-top or closed. Open tanks will face more evaporation, so heat leaves faster.

So How Long Can Tropical Fish Live Without A Heater?

First off, let’s dispel this notion that the temperature dropping is a death sentence to your fish – even tropical fish – unless we are talking about a large drop.

Tropical Fish in an fish tank

Fish can survive low temperatures for some time – an advantage of being cold-blooded. However, it does lower their rate of metabolism and make them sluggish.

Tropical fish can also get stressed without a heater and their immunity will weaken, making them susceptible to infection. 

The reason why we shouldn’t be worried about a large drop in temperature is because it can only drop so far, to the ambient temperature. We’ve seen that room temperature is usually around 70 °F, which is comfortable, even for tropical fish.

The only exception to this is if it is winter and your house doesn’t have heating (or your aquarium is outdoors).

When the temperature drops below 55 °F, tropical fish can live 1-2 days without a heater.

How Long Can a Betta Fish Live Without a Heater?

So do betta fish need a heater? Being a tropical fish, bettas indeed need a heater, unless you are living in the tropics.

Bettas prefer a temperature of 78-80 °F. It is hard to maintain this temperature without a heater in colder climates.When the temperature drops lower, it would not necessarily kill the betta. But as we’ve seen, it can stress the fish and suppress their immune system, which would make them susceptible.

Therefore, when it’s less than 60° F, betta fish can live for a few weeks without a heater. At temperatures below 50° F, they can only live for a few days.

How to Heat an Aquarium Without a Heater

If you think the temperature can drop low enough to kill your fish, it’s time to act fast – use the following methods to heat a fish tank without a heater. 

Use a Hot Water Bottle or Heat Pack

After adding hot water into a bottle or heating a heat pack, you can put them in your aquarium. You may need more than one to get the heating you require.

If it is during a power outage, you can use your stove to heat whatever you have.

Adding hot water directly into the tank is not recommended. It can get too hot and burn your fish.

Moreover, any time you introduce water into your tank, it is a hassle, since you need to make sure it is treated properly (making it free of chlorine for example). 

Use a Heat Lamp

A heat lamp can be fixed on top of the fish tank to provide warmth to it through infrared radiation.

If you do not have a heat lamp you have to resort to using a regular lamp. Incandescent lamps are best since they provide the most heat.

Insulate the Tank

Insulation does not actively provide heat, but it does help retain whatever heat you have for a longer period, keeping your fish tank warm without a heater.

Insulation could be as simple as wrapping thick blankets around your aquarium. Or you could cover the tank with foam. I know this hides your beautiful aquarium from view, but it’s just temporary – you can remove it as soon as you get heating back.

You should also close off the top to prevent heat loss through evaporation. Just make sure you have an air pump to oxygenate the water.

How Long Does a Fish Tank Heater Take to Heat Up?

HITOP 25W 50W 100W 200W 300W Adjustable Aquarium Heater, Submersible Fish Tank Heater Thermostat with Suction Cups (100W-grey)

Say that you got your heater working again, how long does it take to heat the aquarium back up?

Again, this too depends on various factors such as tank size, desired temperature, and the wattage of your heater.

The equation is simple; just divide the specific heat capacity of water by your heater wattage, which gives the time it takes to heat 1kg of water by 1 degree. You can then multiply this number by the mass of water you have and the temperature change you wish to achieve.

Keep in mind that the above equation assumes no heat loss and therefore is an estimate only.

Conclusion

As we discussed, fish can survive for quite some time without a heater. The only time for concern is when the ambient temperature is really low and you have tropical fish such as bettas.

Even then, your aquarium will not lose its heat immediately. The volume of water, room temperature, and insulation all determine how fast the temperature will drop.

You can use this window of time to heat your fish tank using the methods we explored above.

Maintaining the ideal temperature for your fish is vital to keep them healthy and happy – and a failed heater is no excuse. Thanks for reading.

https://pets.stackexchange.com/questions/6730/how-long-can-an-aquarium-remain-without-any-filter-and-heating

https://www.quora.com/If-the-heater-isn-t-working-how-long-will-I-be-able-to-keep-my-fish-alive

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Pet Aquariums

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