Coming from the equatorial regions of Southern Thailand, betta fish are most definitely tropical fish and won’t live for long in cold water.
But what is the optimum water temperature for a betta tank and how long can they survive without a heater? Let’s find out.
What Is the Best Water Temperature for Betta Fish?
Bettas are warmth-loving, equatorial fish and enjoy even warmer temperatures than the average tropical fish. The ideal temperature range for betta fish is between 78-81°F.
This means that, unless you live in tropical regions, you’ll always need an aquarium heater with a reliable thermostat, and a good thermometer to ensure a steady, warm water temperature within the betta’s preferred range.
What Is the Coldest Water Temperature for Keeping Betta Fish?
If you’re considering keeping bettas with other fish that enjoy cooler water temperatures, you may be wondering if you could reduce the temperature of the tank slightly.
I’d advise that, at a push, betta fish could be kept at 76°F, but no lower. Setting your heater’s thermostat so close to the edge of a betta’s safe range leaves little margin for error.
If your aquarium heater breaks or you suffer a power cut, the water would quickly dip into the red, endangering the life of your betta fish.
Can I Keep a Betta Fish Without a Heater?
Unless you live very close to the equator, you should never leave a betta fish tank without a heater!
The average room temperature is only 68°F, which is far too cold for a betta fish to survive.
How Can I Keep My Betta Tank Warm When My Heater Breaks or During a Power Cut?
If your heater breaks or you experience a power outage that might last more than an hour or so, you must act fast to keep your betta warm!
Place insulating materials such as blankets or sleeping bags around your tank, and try to keep the room warm.
Keep a close eye on the tank’s thermometer and add warm water bottles to the tank if necessary.
Be extremely careful about adding warmer water to the tank, since sudden changes in the water temperature can cause thermal shock. We’ll discuss that in more detail in a minute!
How Long Will a Betta Fish Survive in Cold Water?
If your tank’s heater were to break or you experienced a very long power outage, your fish tank’s water temperature would eventually drop to room temperature and your betta fish would be in big trouble!
A betta fish would only be likely to live for a few hours in water under 70°F, so you must do everything you can to ensure this never happens.
Keeping a backup heater in case your main aquarium heater breaks is a good way to guard against disaster.
Checking the tank’s thermometer to ensure a stable water temperature twice a day is also good practice to catch any problems early so that you can rectify them before it’s too late.
How Do I Know If My Betta Fish Is Cold?
If your betta fish becomes too cold, it’ll begin to appear unwell. One of the first symptoms will be a loss of energy, lethargy, and loss of appetite.
Because fish are cold-blooded, they can’t generate their own body heat and a fish that’s too cold won’t be able to metabolize energy as efficiently. A lethargic betta may appear sleepy, resting either at the top or the bottom of the tank.
In general, the top of the tank is a favorite place for a cold betta, since the upper layers of the water are warmer than the bottom of the tank. A cold, lethargic betta at the top of the tank may also make an easy target for other fish to bully or harass.
A cold betta fish is also likely to lose its color and develop a weak immune system. This will make them more susceptible to bacterial and parasitic infections that may then take hold.
What Is the Maximum Temperature for a Betta Fish?
86°F (30°C) is the highest temperature that’s considered safe to keep a betta fish. While most bettas could probably survive slightly warmer water for a short period of time, long periods of exposure to such warm water could prove detrimental to their health, or even fatal.
Warm water is not just a bad idea for your fish. It also speeds up the metabolic processes of all other organisms in your tank, meaning bacteria will consume more oxygen and could leave the tank’s oxygen levels depleted.
Very warm water can even kill your tank’s beneficial bacteria, leading to ammonia poisoning and nitrite spikes – both of which could be fatal to your betta.
How Can I Keep My Aquarium Water Cool in a Heat Wave?
During very hot weather, it’s a good idea to keep an eagle eye on your aquarium thermometer to make sure that the tank doesn’t overheat. This is particularly problematic in nano tanks that can change temperature more rapidly.
To keep your water cool, make the room cooler by keeping the curtains closed, and use air conditioning if you have it.
If you have hot, fluorescent bulbs, turn them off or add a screen to the top of your tank so they don’t heat the water. LED bulbs produce much less heat than fluorescent ones.
In an emergency, you could consider floating a bottle of chilled water or ice in the tank, keeping a close eye on your thermometer every half hour or so.
Be warned, though – ice bottles and ice cubes can change things too quickly, especially in small tanks, and your betta could suffer from temperature shock.
Temperature Shock in Betta Fish
It’s not only constantly warm or cold temperatures that are dangerous for betta fish. If the water temperature changes too quickly in either direction, it can cause thermal shock in your fish, which can often prove fatal.
This is most common when adding a new betta fish to your tank. As it travels from the pet store, the water in its bag can cool down and become significantly cooler than your aquarium’s water.
Experienced fish keepers always float a new fish in its bag, gradually adding mixed aquarium water into the bag before releasing it. We’ve made a dedicated page on acclimatizing a betta fish to a new tank here.
A betta that’s suffered from thermal shock may hang around at the top or the bottom of the tank, breathing quickly, and generally looking unwell.
To avoid thermal shock, never let the tank’s temperature change by more than 2-3 degrees in a 4-hour period. Also, be sure that the water you’re adding to the aquarium when making partial water changes is of matching temperature to your fish tank’s water.
Which Fish Can I Keep Without an Aquarium Heater?
An aquarium without a heater is known as a cold-water aquarium. The fish you can keep in a cold water fish tank are often referred to as coldwater fish.
Cold water fish include goldfish, rosy barbs, gold barbs, bloodfin tetra, Buenos Aires tetra, zebra danios, and white cloud mountain minnows.
Betta fish are definitely not cold-water fish!
Betta fish are warmth-loving fish and prefer a constant temperature of between 78-81°F to remain happy and healthy.
A betta fish will quickly become sick and die in water that’s too cold, too hot, or even in water that changes temperature too suddenly.
A reliable heater and thermometer are your essential accessories for keeping your betta tank within a safe temperature range.
Check out our buyer’s guides to these must-have items by clicking on the links above!