Do Neon Tetras Need a Heater? (Everything You Need to Know)

Aquarium heaters can be one of the most important parts of a neon tetra tank if your house tends to get colder than 75F.

Not having it can cause your fish to get sick and die. At the same time, having it can also cause your fish to die if you’re not careful.

Still, on the whole, if you have a tank, and the water in the tank tends to dip below 75F (either in winter or regularly), it’s a good idea to get a heater.

If your aquarium water seldom dips below the ideal temperature range of the neon tetra, you can probably skip this purchase.

In this article, I’ll cover everything you need to know to select a heater that’s the right size and that’s not likely to fail – as well as where to put it in your aquarium.

Do Neon Tetras Need A Heater?

Neon tetras are a tropical fish. This being said, they need warm water to be healthy and thrive in their aquarium environment.

Whether they need a heater depends on how cold it gets in your house (or wherever you’ve put their aquarium).

Tetras should be kept in water that ranges from 75 to 80 degrees Fahrenheit. This temperature shouldn’t fluctuate and should remain relatively steady throughout both the day and night.

Gentle, gradual fluctuations within the safe range of temperatures for neon tetras can be okay, but if your temperature is constantly rising and falling it may be a good idea to grab a heater to level things out.

It’s important to remember that when considering the temperature of your tetra’s water, the room in which the aquarium is located will play into how powerful of a heater you will need to invest in for your aquarium.

For example, if the aquarium is in a cold basement and you need to raise the temperature from 68F to 78F, your heater will need to be bigger (more watts) than if you only need to raise the temperature a couple of degrees.

If your aquarium is in the upstairs of a room that sees a lot of direct sunlight and natural warmth, your heater probably won’t need to be as powerful to maintain the same target temperature.

To monitor this, be sure to include a thermometer in your aquarium.

You can buy heaters from most pet supply stores. You’ll typically have the option of choosing from a variety of brands. Some of the most common heater brands are Top Fin, Tetra, and Aqueon.

These name brands tend to be more expensive than off-label brands but are known for their durability and reliability, so it may be worth the splurge to invest in one of them.

Cheap heaters can fail and kill all of your fish, so it’s better to invest in a quality one. The price of replacing your fish is almost certain to be more than the price of a good heater.

How Big of a Heater Do Neon Tetras Need?

As I mentioned above, how big of a heater you need depends on how large your aquarium is and how many degrees above room temperature you want to maintain your aquarium.

To raise the water temperature of your aquarium by 5 degrees F, use a heater that is roughly the size of your aquarium in gallons multiplied by 3 for how many watts it is.

For example, you would use a 15 watt heater for a 5 gallon aquarium. 5 gallons x 3 = 15 watt heater.

It’s also okay to use a multiple of 2 instead, such as a 10 watt heater in the above example.

If you need to raise the temperature of your aquarium by 10 degrees F, use a heater that is roughly 10 times the size of the number of gallons in your aquarium for how many watts it’s rated.

For example, if you have a 20 gallon aquarium, use a 200w heater.

You can probably get away with going as low as 5 times in this case as well. So instead of using a 200w, you could get away with a 100w heater.

When in doubt, you should err on the side of a heater that isn’t quite as powerful. This will protect your tetras in the event the thermostat in the heater fails to shut the heater off.

How to Protect Your Neon Tetras Against Heater Failures

It isn’t only cheap heaters that can fail. Even name brand heaters such as Aqueon have been known to fail.

There are two ways a heater can fail. They can fail off, or they can fail on.

If a heater fails in the off position, it will essentially be as if you never had a heater in the first place. Your aquarium will slowly cool down, and your fish will suffer. (But they may survive.)

The more catastrophic type of failure is when your heater fails in the on position. This basically causes the heater to run non-stop without caring that it already raised the temperature in your aquarium to the proper level.

When this happens, your heater can quickly cook all of your fish to death.

Unfortunately, heaters usually fail in the on position, so when (not if) your heater breaks, it’s going to try to kill all of your fish.

There are a few ways you can protect your neon tetras (and other fish) against a heater failure.

If you’re going with a single heater, it’s best to get an external temperature controller. This is something that you plug your heater into that has a thermostat that goes into your aquarium.

If your aquarium’s water drops below the set temperature, the controller will send electricity to your heater. When it reaches the temperature, it will turn the electricity off.

This will provide redundancy in the event that the thermostat in your heater ends up failing.

This doesn’t do you much good in the event your heater fails in the off position, however.

This brings us to our second option. Instead of buying one heater that’s 2x the number of gallons in your aquarium in watts (e.g. a 20 watt heater for a 10 gallon aquarium), you’d buy two heaters that are the same number of watts as your aquarium has gallons.

So instead of buying a 20 watt heater for a 10 gallon aquarium, you’d buy two 10 watt heaters for your 10 gallon aquarium.

Put them on opposite sides of your aquarium, and they will protect you against heaters failing in the off position or failing in the on position either one.

If one fails in the off position, the other will keep running and providing your aquarium at least a little heat. If one fails in the on position, the other one will stay off so that your aquarium doesn’t get quite as hot.

In either case, it provides you more time to realize something has gone wrong and replace the heater.

This is why it’s important to have a thermometer in your aquarium, so you can keep an eye on the temperature your tank’s water is.

Using one or the other of these solutions may sound like it isn’t necessary, but I have heard of a surprising number of cases where a heater has failed and ended up killing all of the fish in an aquarium someone had been working on for years at a time.

Imagine taking care of fish for 4 years only to have them all die because your heater failed. :(

What is The Best Type of Aquarium Heater for Neon Tetras

Generally speaking, you should avoid getting a glass aquarium heater. These are generally cheap and prone to breakage or leaking.

Instead, you should either get a titanium or black plastic heater. Either one will work, though the black ones generally look better.

You also want to make sure you get a heater from a well known brand such as Fluval. This will give you the best chance of having a heater that works in the long run.

If you can’t find a fluval heater, cobalt aquatics also makes a good quality heater.

Where To Put A Heater In A Neon Tetra Aquarium

The goal of placing an aquarium heater is to make sure the water is warmed evenly throughout your aquarium.

When the heated water is evenly dispersed, the temperature of the aquarium will remain stable and there won’t be any spots that are significantly colder or warmer.

The best place for a heater to be placed in a neon tetra’s aquarium is near the aquarium’s filter. This helps to ensure that once the water has been warmed up by the heater, it is evenly dispersed throughout the rest of the aquarium by the flow of the water coming out of the filter.

In most cases, this is where you will want to keep your heater.

If you have a large aquarium, you may be able to find a canister filter that has a built in heater. This will keep the heater out of the aquarium where it isn’t going to be an eyesore.

If you have an all-in-one style aquarium (like the Fluval Flex or Evo tanks), the heater is typically best placed in the chamber where the pump sits. Read the manual on the aquarium if you still have it, however, to see if they intended it to go somewhere else.

Should You Leave An Aquarium Heater On All The Time?

Aquarium heaters should be left on all the time. As a general rule of thumb, if your fish requires a heater, then the heater should never be turned off. Most aquarium heaters have a built-in thermostat that turns them on and off automatically as the temperature of the water changes.

The heater will turn on when the water temperature drops below the set temperature and then off when it starts to become too warm.

Because of this handy feature, you should leave your heater running 24 hours a day.

That isn’t to say that you can just set it and forget it forever, however.

It’s easy to assume that you can just leave your heater to do its thing and not worry about it. However, you should check your heater regularly to ensure that it’s functioning properly.

This is also why we recommend having two thermometers within the aquarium that are each half the wattage your aquarium needs. The two thermometers will almost never fail at the same time, so you’ll always have at least one that’s working properly.

It’ll also make sure that if one fails, it’s easier to tell that something’s wrong without killing all of your fish.

For instance, your heater is set to 78 degrees but the water is colder than usual (according to the thermometer in your aquarium). This indicates that one of your heaters has failed in the off position and you need to figure out which one isn’t working and replace it.

If your temperature is reading higher than usual, on the other hand, you need to check whether one of your heaters is failing to turn off when it should and replace it.


If your house tends to get colder than 75F during the winter (or at night, or whenever), it’s probably best to get a heater for your aquarium if you have neon tetras.

Avoid just going to your local store and picking up whatever heater has your tank’s size printed on the box, however.

A lot of these heaters are oversized and are just waiting to fry your fish as soon as the thermostat breaks. You’ll typically want a heater where the number of watts is 2-3x the number of gallons in your aquarium.

For example, a 20-30 watt heater for a 10 gallon aquarium is properly sized unless you’re keeping your aquarium inside of a freezer.

You can also go with 2 heaters that are half power to protect your self in the event one fails.

If you do this and go with a good brand heater, you’re likely to keep your neon tetras healthy and happy for years to come.