Fish Tank Heaters: When to Use Them and When to Ditch Them

I used to keep fish aquariums with my Dad when I was little. We researched all sorts of tropical fish, and the temperature ranges their environments needed to be kept in. I’ve recently started keeping fish again and decided to brush up my tank-heating knowledge.

When do you need a heater and when don’t you? Most fish tanks will need a heater because most fish require temperatures that cannot be maintained without the use of one. This is especially true of tropical fish, but it is also true of many other varieties of fish. There are some cold water fish that can survive in temperatures as low as 60 degrees Fahrenheit, but depending on your climate and tank placement, you may need to keep a heater for them as well.

Some fish are hardier than others. Some are very sensitive to their environment. Now that we know we need to have a heater regardless of what populates our tank, what else do we need to know about heaters and their usage?

When You Need a Fish Tank Heater

Most fish, be they tropical or not, require temperatures that cannot be maintained in the tank without the use of a heater. When adding fish to your aquarium, you should always look up that specific types water temperature preferences. Some fish are very particular, while others will have a wider range.

Most fish cannot handle drastic changes in their temperature, and it doesn’t take long for a fish tank to be impacted by temperature fluctuation. The smaller the tank, the more quickly it would be affected.

If you live in an area with cold winters, a fish tank heater is recommended no matter the type of fish you have. This is especially true if you keep your fish tank near a drafty window or in a part of your home that experiences fluctuations in temperature.

It never hurts to have a fish tank heater as long as it is set properly and maintained well. You can set it to the optimal temperature for your fish, and it will only run if the water falls below that temperature, so you don’t have to worry about wasting electricity.

When a Fish Tank Heater Isn’t Necessary

A fish tank heater is always a good idea because a drop in your tank temperature will have a negative impact on the health of your fish, but if you’re dead set against having one, there are a few species of fish that you could keep that could handle colder temperatures.

Here are a few examples:

  • Common goldfish
  • Common guppy
  • Clown Load
  • Koi
  • Pufferfish

Unfortunately, if you don’t want a heater, you’re limited in the types of fish you can keep. Common goldish and guppies can still make for a beautiful fish tank, but you have to stick the common varieties.

What Temperature do You Need to Maintain your Tank?

Although the guidelines mentioned above are pretty safe for the majority of fish, there are more things to be considered overall in aquarium temperatures. Some fish, like Guppies, Neon Tetras, and Angelfish need consistently warm temperatures to remain healthy and happy. Others, like Barbs or Swordtails, are a bit more hardy and can tolerate some change.

For example:

  • Most tropical fish: Require their water to be between 74-82 degrees Fahrenheit.
  • Discus: These tropical fish are pickier when it comes to temperature and require a habitat between 82 and 86 degrees Fahrenheit.
  • Goldfish: The staple of any aquarium, Goldfish, are more tolerant of temperature fluctuations, and common varieties can handle temperatures as low as 62 degrees Fahrenheit.
    • Fancy Goldfish: require 68-74 degrees.
    • Comets and Shubunkins: can do well in temperatures as low as 60 degrees Fahrenheit.

Don’t forget that your local pet shop aquarium specialist can provide you with some great information and suggestions as well.

Once you decide on who you’re going to invite as a guest to your tank, you’ll know much better how to heat their home. Now that you’ve decided who’s moving in, what’s next?

How to Determine What Size Heater You Need 

Tank size is a big consideration when it comes to how you’ll maintain and monitor your water temperature. Think of a large living space: one small heater isn’t going to be very effective in reaching and maintaining a livable temperature. You would probably want to invest in two or more heaters.

According to ThatPetPlace, a good rule of thumb is three to five watts per gallon. To not only heat it up to the right temperature but also to maintain it, you’ll need to be sure the heater has enough power to affect the number of gallons in a tank.

As a guideline, a 65-gallon tank will need a heater capable of 200-300 watts. Following that logic:

  • 65 x 3 watts/gallon=195 watts total
  • 65 x 4 watts/gallon=260 watts total
  • 65 x 5 watts/gallon=325 watts total

How Many Heaters do You Really Need?

Now that we know how much power you need to heat the tank, how many heaters do you need to achieve it? It’s recommended that two small heaters be used instead of one really strong one. If you use a 100-watt heater in a 10-gallon tank, you’ll likely cause harm to your fish.

Not only does having more than one heater help keep the entire volume at an even temperature, but it also means you have one as a back up in case one of them fails. A rapid decrease in temperature can cause your fish to go into shock. Tropical fish are really susceptible to changes in water temperature and can cause very serious if not fatal effects.

So, where do we put all these heaters?

Positioning Heaters in Your Tank

It’s best to put the heaters on opposite sides of your tank. Make sure the heater tube length matches the height of your aquarium. Keep in mind that heat rises, so it will be important that the water is heated from the bottom to the top.

Not only do you need to consider where you are positioning your heaters, but be mindful of where you are positioning your tank as well. If the outside air is significantly colder than that of the water, that has an impact on how difficult it will be to maintain the proper temperature. Consider if it is direct light, beneath a heating or cooling vent; these are all factors that impact water temperature.

It’s very important that you monitor and check the temperature to be sure that it is consistent. Remember, a sudden change in temperature is just as dangerous as keeping to low or high of a temperature.

Taking Care of Your Investment

The heater is arguably one of the most important pieces of equipment in any tank. It is important that you take care of it and monitor it.

Read the manual. The easiest part of taking care of the heater and tank is to simply take time to read the directions that accompany your new heater. It’s crucial that you are aware of any maintenance or cleaning the unit may need overtime to keep it in top working condition. It’s also vital to know where to place it within the tank, as well.  Directions are there for a purpose, so be sure to use them.

Check tank temperature to make sure the heater is working. Even when you have the heater set up correctly and functioning perfectly, it’s important to check the temperature of the tank. Thermometers are relatively inexpensive and will help you spot trouble before it’s too late. 

Clean the heater to avoid salt creep. Don’t overlook the fact that fish tank heaters need to be cleaned routinely, especially keeping it clear of Salt creep.Salt creep is the term for the white build-up from minerals in the water. Believe it or not, this residue can build-ups quickly, and it can leave your unit caked with it in just days! Once this develops, it can take quite a bit of effort to remove. This mess can be avoided by maintaining the tank water level and avoiding bubble wands or air rocks in the tank.

Always keep your heater in the water when it is on. Be sure to unplug the fish tank heater anytime you change the aquarium water or remove it from the water. The heater must remain submerged at all times to maintain proper function and avoid shattering.

Try out some temperature monitoring apps. In some cases, there are even apps that can be used to monitor the temperature of your aquarium when you are away from home for a prolonged period of time. Fish Bit is a really cool app that allows you to not only monitor temperature in realtime, but also the overall activity of your fishy friends. In fact, additional equipment can be purchased for use with your Fish Bit to completely automate all the maintenance and upkeep of your tank, allowing you peaceful enjoyment.

What Type of Heater Should You use?

There are a lot of different types of heaters you can use. The most common four are as follows:

  • Submersible
  • Immersible
  • Substrate
  • Filter heaters

Each of the types listed performs the same basic function – getting the water to the desired temperature and maintaining it there – but they do it in different ways. Any of them could work for you, honestly. Let’s talk about the different types.

Submersible Heaters

These heaters are made to be submerged (just like the name implies) into the water where the fish live. Submersible heaters are long cylinders that are commonly stuck to the side of the tank with a suction cup. They are meant to be so that the bottom does not come to close to the gravel at the bottom of the tank. Gravel isn’t a great heat conductor and could cause cracking in your unit.

These are usually more efficient than other types of heaters, given that they are completely in the water. You can place it as deep as you need within the tank, making the most of the heat it radiates. If the variety you’ve selected has an internal thermostat, it is best placed horizontally. In that position, it will give the most accurate readings, switching the heat source on and off at the correct times.

The Aqueon Pro Submersible 50W Heater is a very popular brand that can be used with both salt and freshwater tanks. It’s also completely shatterproof and contains no glass at all. It’s aluminum.

Another great option is the  Fluval M Submersible Heater. These heaters are super high tech and offer an LCD screen featuring a realtime temperature of the tank. Another great feature it contains is a flashing LCD display grabbing your attention when the water temperatures become dangerous. Exclusive mirror technology inside of the unit reflects the colors of your aquarium, keeping it visibly appealing as it works as well.

Immersible Heaters

These varieties are usually a glass tube housing a heating element wound around a ceramic or glass insert. Some of them also have sand or other conductors inside allowing them to be placed mostly underwater.

More commonly known as hanging heaters, they hang from the top of your tank but cannot be completely submerged in the eater. There is a clear mark on the side of the unit depicting where the waterline should be. It’s important that they are not submerged any deeper than that, It’s also important to make sure the length meant to be underwater remains as such, or shattering can occur.

A good starting model is the Eheim Jager Aquarium Thermostat Heater available on Amazon. These units are made from 50 watts to 300 watts apiece.

Substrate Heaters

Substrate heaters, like the Hydor 25w Hydrokable Substrate Cable Heater, are made with a flexible cable with a heating element that can be placed below gravel or sand. Also known as Cable heaters, these units are unseen in the tank because they are completely buried in the floor.

Although these are the least common heating apparatus used in tanks, they are perfect for planted tanks where the gravel or sand tends to keep the roots of the plant life cooler than the rest of the water. If you don’t keep plants in your fish, this is probably not your best option. They tend to be the most difficult to install and maintain.

The cable heats and serves to heat the gravel, which in turn radiates heat and arms the water. By heating the gravel, it maintains warmth to the roots of your underwater plant life, keeping them at a comfortable temperature to thrive and grow.

The best method of placement for these heaters is to place them in a zigzag formation along the bottom of the tank, spreading the heat element throughout the entire bottom of your tank. This provides the most even heating.

Filter Heaters

Although they are by far the pricest option, thermo filters are quite effective in improving the overall health of your tank. These units heat the water as it goes through the filter itself, not only cleaning the water by filtering out debris and toxins, but also maintaining perfect temperatures.

A great example of a filter heater is the OASE Indoor Aquatics Filtosmart Thermo. This model comes in 100, 200 and 300-watt varieties. This variety would be the lowest-maintenance of the four, but again, the price reflects that.

Fish Tank Heater Installation Tips

Now that we have explored the different types of heating sources for your tank, there are a few more things to be considered. To be sure that you are getting the most out of your investment, let’s take a look at a few of those.

  • Allow the heater to acclimate to the temperature of the water. When you install the heater, whether it be under the gravel, on the side, or submerged, you need to give it ample time to acclimate to the current temperature of the water. This can be done by simply leaving it in the water for a substantial amount of time, typically an hour, before powering it on. This keeps the glass from being shocked by the change in temperature, potentially shattering once the heating element comes on.
  • Allow the heater to cool down before removing it from the tank. When removing the heater, turn it off or at least an hour prior to removing it from the water. If you take it out too quickly, the change in external temperature could cause the heater to shatter, contaminating your tank and putting the life of your fish in jeopardy. It would also force you to do a complete draining and cleaning of the tank. In addition to all that mess, it prevents the heater from melting outside surfaces you place it on once you remove it.
  • Make sure that the glass of the heater is not touching the side of the tank, the gravel, or any ornamental fixtures you have inside. Again, this helps from potentially shattering the heating unit or electrocuting your fish. Click here to see a variety of different guards that can be purchased to avoid this from happening.
  • Make sure your fish can’t get stuck between it and something else. The best way to avoid that is to ensure that your fishy friends have plenty of plants or other ornamentation to hide in, making the heater the very last option. Using the heater to hide can cause burns and other dangers to their wellbeing. Fish can be shy by nature and need a bunch of places they can hide to feel safe. A heater is not a safe choice.

So Now What?

We’ve gone over the absolute necessity of heating your tank, even if it’s just a carnival goldfish, as well as plenty of food for thought in how you can provide that heat to your tank.

Fish are one of the most vulnerable pets you can keep. Dogs, cats, rodents, even reptiles can communicate their needs or discomfort effectively. Fish are unable to communicate their environmental discomforts. In addition to that, their environment is completely separate for your own, which means subtle changes in temperature or water quality are not detected by you.

To not only protect your investment but also ensure the best quality of life for your fishy friends, it is of the utmost importance that you are monitoring and adjusting their environment to keep the best possible living conditions for them. Fish can bring years of stress-relieving enjoyment to you and your family as long as you take great care of them. If you still are unsure about your ability to caretake for an aquarium, start with a hardier breed that allows for you to have a learning curve. Before taking on a saltwater habitat, maybe keep a guppy or two. Before long, you’ll be an expert.

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Adam Edwards
Hi, my name is Adam and I'm an aquarium enthusiast! I didn't discover the joys of being an 'aquarium fanatic' (as some of my friends call me!) until I was in my 20's. When I first started out I found it difficult to find all the information I needed so I started this website to compile all the useful information I can think of. Enjoy!