Can a Fish Tank Heater Kill Fish? What We Have Experienced So Far?

A heater keeps a tank from becoming too cold. Throughout the day, the temperature of the fish tank remains constant.

The heater must maintain the tank’s desired temperature at all times. This should be maintained even when the room is at its coldest.

Many individuals, however, are unsure whether or not putting a heater in a fish tank is safe. If you’re looking for a direct answer, the answer is yes, it’s safe.

However, if there are any complications, the fish may be harmed. Continue reading to find out more about the heaters used in fish tanks and their effects.

Does the Water Heater Harm/Kill the Fish Inside a Fish Tank?

In most cases, the temperature of the water will not harm the fish.

However, if a fish comes into close contact with your fish tank heater, it might burn. Fish tank warmers are made to be as safe as possible for the fish.

The fish might get harmed if it touches the heater. But a fish being ‘burnt’ by a heater is extremely unusual. But that doesn’t make it any less of an issue.

You may take safeguards if you are concerned about this occurring to your fish.

The best option is to cover your fish tank heater with a plastic covering. The majority of fish tank heaters include built-in safety features. It will help keep your fish tank cool and prevent it from overheating and catching on fire.

What are the Signs of a Fish Injured by the Heater?

If your fish becomes trapped and gets burnt by the heater, it will learn to avoid the heater.

If the fish does not display any signs of harm while moving, it may be more difficult to notice. A burn mark may be seen on the fish’s skin.

The burn mark on the fish will initially appear to be negligible. The skin will appear to be white. The gills will also appear more translucent. After a few days, if the fish has been badly burnt, the wound will seem even worse.

Predators or other fish might also attack an injured fish. So, if you notice that any of your fish is injured, separate it immediately. Then, you should try to heal it back to normal.

Why Does the Fish Tank Heater Fail?

Low-priced heaters tend to break down. The connection that turns the heater on and off may sometimes become locked. This is the most common cause of a fish tank heater failure.

The contact becomes locked in one of two states: on or off. In the first situation, your tank may become quite hot. This might be a concern, especially if the heater is bigger than your tank requires.

Ignore heaters that are greater than your tank’s recommended size to avoid potential complications. Instead of one huge heater, use two smaller ones in tandem to avoid winter calamities.

What is the Safest Fish Tank Temperature for the Fish?

There is a range of temperatures where all fish thrive. The fish may suffer if the fish tank heater malfunctions and the temperature rises or falls too much.

Tropical fish thrive best when the temperature is between 24 and 27 degrees Celsius. Temperatures between 15° and 24 degrees Celsius are ideal for cool water fish.

If the temperature of the water exceeds 32 degrees Celsius, problems arise. Your fish will need more oxygen in warm water. These fish can become lethargic and sluggish at cooler temperatures. As a result, they may die.

Here is a chart showing the ideal temperature for several fish species:

Fish TypeAppropriate Temperature
Saltwater Fish24 – 27° C
Rosy Red Minnow10 – 25.5° C
Tropical Fish24 – 27° C
Bloodfin Tetra18 – 28° C
Sunset Variatus22 – 28° C
Cichlid Tank24 – 27° C
Fancy Goldfish10 – 18° C

Maintaining the given temperature should ensure that the fish won’t be harmed. Set your fish tank heater’s thermostat following the fish’s species. The fish may die if the temperature rises too high.

How to Cure a Fish Injured by a Fish Tank Heater?

You may lower the osmotic pressure in your fish tank by adding salt. For every 38 litres of water, add around 6 teaspoons. Excessive salt in the water should be avoided.

You may use either plain table salt without additives or fish tank salt. Use a smaller tank for the salt treatment if you have one available. If it doesn’t work, you may treat the main tank, but that will require more salt.

You should also change 20 percent of the water daily until the fish’s wound appears to be healing. The ammonia and nitrate levels will be kept low by doing these extra water changes.

If the cut is severe, your fish may not survive. Other illnesses can spread from a wound that has been burned. Water changes should be done regularly.

Should I Leave The Fish Tank Heater On All the Time?

Yes, if the water must be kept warm for the fish. Heaters for fish tanks are made to be left on 24 hours a day. If the heaters reach a certain temperature, an inbuilt thermostat cuts off the heat.

The thermostat maintains the temperature of the water within a few degrees of the specified temperature. The heater must be left on to keep the water in your fish tank at a consistent temperature.

The constant power also ensures that the water does not fluctuate too much. Fish and other aquatic species can be stressed by fluctuating water temperatures in their tanks.

Fish tank heaters do not require regular replacement for years if you leave them on 24/7. So, don’t be scared of burning it out. You can replace the heater if it has been damaged by power surges.

How to Keep the Fish Safe from the Heater?

There are several ways to safekeeping fish inside a fish tank. Follow the instructions given below:

  1. Buy a good quality heater with a built-in heater guard.
  2. You can also make a heater guard by yourself by following this procedure.
  3. Always inspect the thermostat and set the temperature according to the type of fish.
  4. Disconnect the heater while changing position and temperature.
  5. Install a heater with heatproof wiring.

The probability of the fish getting injured by the heater will decrease heavily if you manage to perform all of these procedures.


A heater is not always required for the fish in the fish tank. But some species need the heater to live normally. Most of the heaters are safe to use. The fishes are also smart enough to avoid the heaters.

If they get burnt, follow the mentioned instructions to cure the fish. You should also take measures to prevent further damage to the fish.

Buy the heaters that provide the best safety features to prevent injuries. With top-quality heaters, you can be sure that the fish will be safe.

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Arif H Fahim

Welcome to PetFishTank! My name is Arif. I make an effort to publish educational articles using my many years of expertise as a fish owner.

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