betta fish experiencing temperature shock

Betta Temperature Shock Symptoms

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While all the parameters in your betta fish tank might check out, if the water temperature is too high or too low, there is a chance that you could severely injure or kill your fish. Temperature shock is the result of a deviation from ideal water temperatures, either caused by temperatures changing too much or too quickly. It is important to know the signs of temperature shock and know how to fix the problem immediately as this can quickly lead to the death of your betta fish.

Keep reading to find out everything you need to know about temperature shock, symptoms of temperature shock, and how to fix it if it happens in your own freshwater betta aquarium.

What is temperature shock?

red betta fish in the bottom of aquarium

Temperature shock is the physiological response to sudden or large changes in temperature. This can lead to the ambient body temperature rising or falling respectively; in humans, this is similar to hypothermia and hyperthermia.

For fish, temperature shock can also happen when the water temperature suddenly or drastically changes. If the fish is unable to adapt or if conditions don’t improve, the body will fail to function properly and start to shut down.

What causes temperature shock?

Temperature shock can happen when the water temperature deviates too quickly or too much from ideal conditions. This can happen either when the temperature goes too low or too high, though colder temperatures are more likely to be the culprit for bettas and other tank life.

Most fish sold in the aquarium hobby are tropical fish, meaning that they need tropical water temperatures to be able to perform necessary bodily functions. However, there are a few ways that temperature could change and lead to shock.


When you bring home a new fish, it is recommended to either drip acclimate or add tank water to a container with the fish for up to an hour or more; this process helps the fish adapt to any changes in water parameters, like pH levels and nitrates. However, it is first advised to float the bag with the new fish for up to 30 minutes before this process.

When floating the bag, the water temperature inside the bag is adjusting to the temperature of the tank at a moderate rate that your fish can handle. Once temperatures have been matched, the other parameters can then be matched as well; the addition of tank water to the container will help keep the temperature constant while balancing other parameters. Failure to acclimate new fish to a tank causes the body to go into shock if conditions differ too much.

Remember that it is even better to add new fish to a quarantine tank before adding them to the main display to limit the chances of introducing disease and/or parasites!

Water changes

Similarly, water changes can cause fish tank temperatures to suddenly fluctuate, especially if performing a larger change. When doing a water change, it is best to prepare the new water ahead of time, dosing a water conditioner and using a heater to match temperatures with the main tank display.

By heating up your water before a water change, you lessen the chances of temperatures changing too much as well as from creating pockets of different temperatures within the tank. Physically, cold water is denser than hot water and the water column can become striated, or separated, depending on temperatures. While the flow in your tank will quickly mix the two, one of these pockets could be enough to affect your fish or invertebrates!

In addition, adjusting the temperature of new water before a water change will help keep equipment from overworking. If one of these cold patches passes your heater, it will turn on in attempts to raise the temperature. Likewise, hot water should be cooled down before being added to a tank.

Changes in room temperature

It is always good to have an aquarium heater even if you are keeping coldwater species, like goldfish, or if your climate is known to stay relatively the same. Changes in room temperature directly influence the water temperature of your tank and can cause large swings if left unregulated, especially in smaller tanks.

If living in especially hot climates, it may even be worthwhile getting some fans to put over the tank or purchasing an aquarium chiller.

Faulty equipment

Lastly, temperature shock could be caused by faulty equipment, which is a common problem. Heaters are notorious for spontaneously quitting overnight, either failing to turn on or overheating the tank entirely.

Unfortunately, there is not much you can do to prevent tank equipment from failing. Buying a reliable brand, regularly making sure that everything is working as it’s supposed to, and keeping an eye on daily temperature fluctuations are all you can really do to make sure equipment is functioning properly; some hobbyists even have backup heaters and coolers that are connected to their cellphones for such an emergency.

Possibly just as important as a good aquarium heater, an accurate thermometer for your tank will let you see the problem as it’s happening. External thermometers are known to only read a mix of the tank temperature and room temperature, usually leading to false readings. Analog thermometers usually suffice for most aquarium setups, but a digital one is even better at offering exact readings.

If you do find yourself waking up to a cold or overheated tank, try to approach the problem swiftly and calmly and hope that your betta and other tank life can be saved!

What is the right temperature for your betta fish?

While bettas are usually kept in small containers at the pet store, they are actually tropical fish that need a heated tank in order to survive. That being said, the best betta temperature is between 78-80° F (25.6-26.7° C).

It is important to note that betta fish are cold-blooded, which means that they are not able to physiologically regulate their own body temperature. Instead, they are dependent on their environment to keep them at the right temperatures for biological processes to fully function.

For more information about the best betta tank setup, make sure to check out our ultimate betta guide here.

How do you know if your betta fish in shock?

One of the best ways to know if your betta fish is experiencing temperature shock is by checking the water temperature of the tank with a reliable thermometer. If the water temperature is drastically out of the ideal range (+/- 10 degrees), then you’re most likely dealing with a sick betta.

However, if you are unable to immediately check the temperature of the tank, it is good to know betta temperature shock symptoms and how to care for an affected fish.

What happens if your betta fish gets too cold?

There are a few signs of tank water being too cold for too long, like loss of color, lethargy, and disease. Cold temperatures usually affect bettas more and all of these symptoms could be fatal if not treated immediately.

Loss of color

Loss of color is usually one of the telltale signs that something is wrong in your aquarium, and all water parameters should be tested immediately. Along with the loss of color, female bettas might even develop stress stripes, which is indicative that conditions are not optimal.

Once the temperature has been fixed, it might take several weeks or months for your betta fish to lose its stress stripes and gain back its color entirely.


When temperatures drop, betta fish metabolism slows down in order to conserve energy; metabolism is what allows organisms to convert food into energy for essential bodily functions. When this slows down, bodily functions also slow down.

This means that your betta fish will usually stop swimming, eating, and might even have a reduced breathing rate. As a result, it is common to see your betta fish resting on the bottom of the tank or on other plants and decorations around your aquarium. If your betta fish is unable to lift itself off the gravel, there is a chance that it could develop fin rot. Treatment for fin rot may be found in this guide.

More susceptible to disease

Because of this slowed metabolic rate, the immune system is compromised. This means that your betta fish is much more likely to contract a disease or be otherwise infected with parasites like ich. Even more so, it means that your betta fish will often not be able to fight back the disease or infection on its own; even the best hospital tank might not be able to bring back your betta as medications can further stress out a sick fish.

Identification and treatment of ich can be found here.

What happens if your betta fish gets too warm?

Though betta fish tend to react more drastically to cold temperatures, warm temperatures can become just as dangerous and just as quickly. You will want to look out for signs of rapid breathing, swimming at the surface, and otherwise erratic swimming.

Rapid breathing

There are a few reasons why warm water makes breathing more difficult for fish. First, warm water cannot hold as much dissolved oxygen as might be needed for regular physiological functions. Secondly, warm water causes the metabolic rate to increase; this meaning that the body needs that much more oxygen, and the fish tries to compensate by breathing more rapidly.

As a result, the heart and inclusive cardiovascular system cannot keep up with how much blood and oxygen need to be pumped throughout the body, leaving the fish to ultimately suffocate.

Swimming at the surface

Some betta fish like to stay at the surface of the tank, and it’s even normal to see them go up for air every once in a while as they are anabantoids, which means they can use their labyrinth organ to breathe atmospheric air. However, if you notice that your betta is struggling to stay up at the top of the tank but chooses to do so anyway, there is most likely an underlying problem.

As mentioned before, warm water holds less dissolved oxygen. As gas exchange happens at the surface of the water, dissolved oxygen concentrations are highest in the top layer of the tank. This behavior may also be accompanied by heavy breathing and erratic swimming.

It is important to note that seeing bettas breathing rapidly and swimming at the surface may also be indicative of ammonia or nitrites being present in the tank.

Erratic swimming

Erratic swimming could be the result of your fish trying to escape from less-than-ideal water conditions. Warm waters and lack of oxygen can lead to disorientation, which could cause your betta fish to bump into the sides of the tank and any other decorations. It could also cause your fish to swim up and down the water column or side to side.

Unfortunately, this can quickly lead to over-exhaustion; as before, your betta might not be able to lift itself off the bottom gravel and fin rot can develop. If you think that your betta fish is acting out of its normal behavior, make sure to test all important water parameters.

How to correct temperature shock

The problem with fixing temperature shock is that it needs to be done immediately over time; it is crucial to reduce or increase the temperature as soon as possible, but making sudden changes can also just stress out your betta fish even more.

Reducing water temperature

betta fish temperature

For reducing water temperature, it is best to reduce in increments of 2-3 degrees every 4 hours; some hobbyists even believe that a 2-3 degree reduction every day is even better, in the case of an emergency, you do not have that time.

First, make sure that the aquarium heater is working properly. If it is, then set it to an ideal temperature; the heater should not be completely turned off as this can lead to the aquarium cooling off too quickly. Next, turn off the tank light and open the hood of the aquarium; this will stop any heat being transmitted from the lights and allows for greater evaporation. Any windows or other sources of light should also be blocked or shut off. Fans can be added to the top of the tank to further improve evaporation rates.

Small bags of ice may then be floated in the tank; still, make sure that you are not reducing the temperature too quickly; never put the ice cubes directly into the tank as this can upset water parameters, and is much less controllable than if in a bag.

Small water changes with cooler water may also be used to help lower the temperature, though the amount needs to be carefully calculated in order to avoid lowering the temperature too much; a small water change can also help if there is ammonia or nitrite in the water column, though too large of a water change can stress your betta out even more.

An air pump may also be used to help keep oxygen moving into and throughout the tank.

Increasing water temperature

Bettas seem to be affected more quickly and greater by low water temperatures than water that is too hot, so it’s important to address symptoms immediately. However, it is still recommended to only increase the temperature a couple of degrees every several hours to prevent your betta from stressing out too much.

Unfortunately, there are not too many ways to accurately heat a tank back up. The best way is to program an aquarium heater with the appropriate temperature and keep an eye on the thermometer to make sure that the change is gradual. A small water changes every 4+ hours with warmer water can also help gradually raise the temperature if possible.

In the case of a power outage, towels and blankets may be wrapped around the tank to keep heat from escaping as much. An air pump should also be added during this time in order to keep oxygen circulating. Otherwise, hand warmers may be placed in a plastic bag and floated on the surface of the water; be sure to read the instructions of the hand warmers before use as some will not work correctly if placed in a sealed bag.

How to help your betta fish recover

Once water temperature has returned to its optimal range, it is time to care for the effect it has had on your betta fish. Temperature shock symptoms will most likely last for a few days, and sometimes even a week or more. During this time, it’s important to keep your betta as happy as possible.

You will need to make sure that water parameters are exact; small fluctuations will hurt your weakened fish more than usual and stability is key. Your betta should be given a high-quality diet to help it regain its strength, and possibly its color. However, don’t be alarmed if your betta’s color doesn’t return for a month or more as this can usually take the longest to recover.

Additional equipment should be purchased in order to change out and/or upgrade faulty pieces. It may be time to get a new heater or even to invest in an aquarium chiller. If keeping a larger system, a backup generator may even be worthwhile to prevent this problem from happening again if it was due to a power outage.

There are also a few other ways to treat your betta and help with the recovery process. One method is to add Indian almond leaves. These organic leaves release tannins into the water which are good for bolstering immunity and the overall strength of the fish. Vitamins, like Boyd Vita-Chem, may also be supplemented to further help with your betta’s recovery.


Temperature shock can be a scary thing for both you and your betta fish. Knowing the symptoms to look out for and being able to immediately fix the problem can help save not only your fish but also your entire aquarium system. Some of the best ways to prevent drastic temperature changes in your tank are by regularly checking equipment, having an accurate thermometer, and examining your fish for injury and/or strange behavior every day.

If you have any questions about temperature shock, temperature ranges in the aquarium, or have had an unfortunate experience dealing with bettas and temperature, don’t hesitate to leave a comment below!

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