How to know if your Aquarium Heater is Working

An Aquarium heater is the most needed piece of equipment inside the tank setup, aside from maybe the filter. The aquarium filter helps provide the optimal environment for your fish. Knowing how to tell if your aquarium heater is working can help you with keeping your fish alive and comfortable all year round.  

How to know if Aquarium Heater is Working:

  1. The Heater has a short in it
  2. The heater is overworked at the moment and just needs to cool off.
  3. The indicator light is not turning on
  4. The heater is not in the correct location
  5. The heater is not the correct size for the tank
  6. The heater is cracked.

Aquarium heaters are designed to heat the aquarium to the desired temperature and then shut off. Chances are that unless your aquarium heater is broken, there are other reasons why the water temperature is not reaching the ideal point. It can be rather tricky trying to determine if the heater is broken or if there is another reason it is not heating up.

How do I know if the Aquarium Heater is Working

The most common issue is not a manufacturer defect; it is having the correct size heater for the tank. In this case, the internal temperature of the water simply isn’t getting enough water flow to maintain the temperature required against the elements within the tank itself.

Aquarium heaters need to be placed in the proper place inside the aquarium to work properly. If the water heater does not have the correct circulation of water, it will take too long to heat up. This causes only a portion of the tank to be heated because the water is not properly circulated.

The Heater can be overworked. It may just need a quick break to avoid overheating the element. Some heaters are made with a glass casing around them; in order to heat up the tank, they must get hotter than the desired temperature for short time periods. It is possible that the heater itself simply is just too hot to work at the moment.

Aquarium heaters are rather sensitive and can short out quickly, and if it was not unplugged during the last aquarium water change, then it may have shorted out. These heaters work by converting electricity to heat, and can easily short out if water gets anywhere near the electrical components that help conduct electricity in the heating element.  

Testing the Aquarium Heater

Visually inspecting the heating element first can save time by determining if there is a clear malfunction in the heating element. Look for any signs of wear and tear that seem abnormal, exposed wires, cracked glass, or discoloration of aluminum parts, are all signs that the heating element is failing.

One of the best ways to tell if the aquarium heater is working correctly is to test the heater in a separate bucket of water.

  1. Get about 2.5 gallons of water, or enough to fully submerge the heater
  2. Measure the temperature of the water before placing the heater in it
  3. Place the heater in the 2.5 gallons of water
  4. Wait about an hour
  5. Measure the temperature to see if there is an increase from the original measurement
  6. Remember to use a glass container; you could even use a drinking glass, or pitcher

If you don’t have any of these materials on hand, you can do the old fashioned hand test with your heater.  Plug the heater in, wait a few minutes, and then approach the heater slowly with your hand to see if it is warm. If there is heat, then the heater is working.

Early Signs of the Heater Being Broken

If you use a thermometer, you may be able to tell that your heater is going out by how often the heater it turns itself on. If you notice that your heater is working harder than usual, this is a clear indicator that something is not quite right. The thermometer will show a fluctuation and a temperature change more often inside the tank.

Another sure sign that your heater is going out is that if the temperature is fluctuating too regularly inside the tank. This can be a sign of an overworked heating element, and you may be better off using two lower wattage heaters in place of the one heater.

If there are noticeable signs of wear and tear on the heating element, it may be time to replace it soon. Sometimes the glass can crack, or chip, the metal can corrode or turn colors, the suction cup can lose its suction. These are clear indicators that the heating elements need an upgrade, don’t wait until it goes out, that could cost some fish their lives.

If you plug the heater in and it doesn’t increase the heat, it is most likely broken. Testing the heater prior to placing it inside the tank is the best way to ensure that it is working. You do not want the heater plugged in without it being in the water. This can break the heater or cause the glass to crack.

Proper Placement of the Heater

The two things that are going to be your best friends are convection and circulation when deciding where to place your heater.  Water is a great conductor of heat, but the majority of the action comes from the ionic bond between the water molecules themselves and how they interact with heat.

As the water heats up, it becomes less dense and rises to the top of the tank, pushing the more dense cooler water closer to the bottom of the tank where the heater is. This keeps the water moving and warm, and convection in combination with circulation helps warm the tank.

Placing your heater near circulation points will help distribute the heated water throughout the tank evenly. Having excellent circulation will prevent any cold and hot zones within the tank. Placing the heating element close to the water filters exit point will help with good circulation within the tank.

If you chose a partially submersible heater instead of a fully submersible heater, then placing an air stone below the heating element can help with circulating the water. The idea is to place the heater where you get great convection and circulation so that the tank is heated evenly.

Reasons I Need a Heater

Aquarium heaters have an important role in the fish’s survival. Fish do not have the ability to warm themselves up; they are cold-blooded, meaning that fish must rely on the temperature of the water to provide them with their body temperature.

Aquarium heaters help regulate temperature fluctuations within the aquarium, allowing the fish to experience a stable environment. Having a steady temperature in the water keeps the fish’s metabolism at the correct level, and helps limit disease.

It is important to have the correct temperature for the type of fish that you have in your tank. Some fish can survive just fine with room temperature water at or below 75 degrees Farienhieght. Goldfish typically do not need a heater, but most tropical fish rely on the heater to keep the environment comfortable.

The temperature in your household changes with the seasons and this can mean life or death for your fish.  In the wild, fish swim to waters that are comfortable for them during different times of the year. In your tank, they are completely limited to the tank; as the temperature changes from cold to hot, back to cold, the change in temperature in the water can stress the fish out.

Types of heaters

Submersible heaters are designed to be placed inside the tank in a low spot close to the gravel. A submersible heater should be kept off of the gravel as it may cause the glass to crack. Placing the heater in a horizontal position is going to yield the best results. This heats the water across the tank, fully allowing the proper convection to take place.

Immersible water heaters or hanging heaters are immersible to the water line on the unit and hang vertically in the tank. These types of heaters cannot be fully submerged and are great for smaller tanks with a top-level filtration system, such as a power filter.

Substrate heaters are known as cable heaters, and these types of heaters are buried underneath the gravel. Substrate heaters heat the gravel and are great for planted tanks where the plant life is a concern. The idea behind this type of heater is that the roots of the plants may not be getting the heat they need.

Filter heaters are a filter and heater combination that heats the water as it passes through the filter. They are more common on canister or power filters as an added benefit.

Inline filters heat the lines for the container filters. The water pumps push the heated water back into the tank.

Picking the Correct Size

Mini heaters are good for heating 1-5 gallon tanks, but should not be used on anything smaller than 1 gallon. You also want to make sure that you select the correct size heater for your tank. Having 2.5-5 watts per volume gallon is what is recommended.

Taking the average room temperature and factoring in the targeted temperature of the tank, you will determine how many heating units you will need to keep the tank at its optimum temperature.

If it is 68 degrees in your house, and you need the tank at 78 degrees, then you are going to need 10 degrees of heating units. You would then need to purchase the correct wattage for reaching that specific level.

 9 degrees F18 degrees F27 Degrees F
10 Gallons5075W75W
25 Gallons75W100W200W
50 Gallons150W200W2/300W

Should I use Two Heaters

Depending on the size of the aquarium, you may want to consider using two heaters inside the tank. One on each side of the tank to lower the amount of stress on one heater. Just make sure that you place them where they are equally distributing the heat inside the tank.

This method is usually used for larger tanks as it is not only more cost-efficient, but it limits the risk of losing fish due to an equipment failure while you are away. The other heater will simply just work harder for the short time frame that it needs to until a replacement can be installed.

Using two heaters minimizes temperature swings inside the tank, and provides a more stable environment for the fish. Drastic changes in the temperature of the water will change the fish’s metabolism rate, which in turn either makes them overactive or underactive.

Two heaters are great for an emergency tank heater or introducing new fish to a tank. Putting the secondary heater inside the introduction tank will get the fish acclimated to the environmental temperature faster, this is really helpful with coral.  

It is recommended to use two heaters if your tank is larger than 40 gallons.  If you are using two heaters, then you would split the wattage in half, allocating the heat load equally between both heaters. Also, it is a good idea to use a wattage one level above with a temperature control module on the heater.

Using thermometers

A tank thermometer placed on both sides of the tank is the best way to determine what the overall temperature is inside the aquarium. You place one on the right front panel, and then another one on the rear left panel, this gives you a full view of the environment inside the tank.

There are different types of thermometers, and depending on the tank size, fish, habitat, and other factors. There will always be a different answer to which one to use. I have found that the glass thermometers are the most accurate for my tanks. However, the digital thermometers are considered more accurate than the standing or floating thermometers.

For smaller tanks, the digital thermometers work perfectly fine and can be picked up cheaply on Amazon. It is recommended to use a thermometer to tell if the environment is correct for the type of fish in the water. Using a thermometer is the only way to tell if the heater is working or not.

LCD Thermometers are the ones that are stuck to the outside of the tank. They work by reading the temperature of the glass that it is attached to. However, this is the least accurate of tank thermometers as they can be affected by different things, such as sunlight, heating vents, or even room temperature.

A Few Things to Consider

When removing any heating element inside the tank, you should unplug it and let it cool down completely before removing it. Leaving the heating element in the water for at least 1 hour to allow it to properly cool down is not only necessary for safe operation, but it can save your tank. If the heating element is hotter than the glass, there is a good chance it can crack your tank.

The inverse applies when setting up the heater for the first time. Leaving it in the tank for a little over an hour allows the heater and the glass to become the same temperature before changing the temperature of the environment around the glass.  Following this method would prevent any catastrophes of introducing a new heating element to your aquarium.

Make sure that your heating tank is well equipped for your fish to find safe places to hide. You don’t want your fish hiding behind the heating element because there were no rocks or plants for them to hide.

Don’t let the heating element touch the glass, gravel, or any ornaments that you have. Nothing should contact the heating element except the water. This will prevent lost fish tanks and ornaments.

How Can I Stop the Heater from Breaking

There is no sure way to prevent your heater from breaking, but there are a few things that you can do to prolong your aquarium heater’s lifespan. Following the manufacturers recommended installation and usage is number one on this list.

Using a multi-way socket, or a power strip, instead of plugging the heater directly into the wall can help prevent short circuits from happening because of a power surge. If using a power strip, make sure that it is mounted to the tank stand in an area where water cannot drip onto it from daily use.

Using a heater guard and purchasing a backup heater can help keep your heater alive longer. The heater guard will provide some insulation between the heater and the glass. This can limit the possibility of a short, or glass breaking inside the tank.

Cleaning your heater regularly can help prevent any build-up around the heating element. Getting the salt off of the element, and other mineral deposits can help improve your heater’s efficiency and prolong its lifespan.

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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!