Betta Fish Swimming In Dark But Not In Light: Why?

Why Is My Betta Fish Obsessed With Filter

One thing about bettas is that they love having sufficient lighting in the tank. You will see them thriving during the day and rest when there’s no light.  That’s why it’s alarming when the opposite happens. By that, we mean your betta suddenly stops swimming in the light.

The tank light might be too bright for your betta. Or, the light produces enough heat to warm up the water and make it uncomfortable for swimming. Apart from that, being new in the tank can cause such behavior as well.

No matter the reason, you must address it as soon as possible. it’s just not normal for a betta to hide in the day-light. There must be something bothering that poor thing. Keep reading if you want to figure it out.

Key Takeaways

  • The tank might be too bright for the fish.
  • If the betta is used to a different sleep pattern, that might be an issue.
  • Bettas don’t like coming out when it has hostile or competitive tankmates.
  • If it’s a new tank for the betta, the fish will need time to adjust.

Do Betta Fish See Anything In Dark?

It depends on what you mean by “dark.” Your betta can’t see anything if it’s pitch black inside the tank. That’s the reason you find the food untouched when there’s no light. In this situation, Betta usually depends on other senses to survive. They use their hearing and smelling senses to identify a possible threat (by changing a sound wave).

Bettas have a vision similar to humans. We mean that the fish can still see under dimmed lighting. They can figure out whether an object is coming their way or not. Bettas can even detect the color clearly once the thing gets close enough. The dimmer the light is, the blurrier their vision gets.

So, it makes sense for bettas to stop swimming or exploring when they can’t even see properly. There’s nothing to worry about.

But what if the opposite happens? Some bettas choose to swim only when the light is out. Is it a personal choice? Or is there something you need to take care of? Let’s find out.

whitish betta fish with yellowish fin

Why Is My Betta Fish Swimming In Dark But Not In Light?

There can be multiple reasons behind such behavior. Without knowing your fish tank’s exact condition, there’s no way we can give a fixed answer. However, we have enlisted possible scenarios that might be causing such weird behavior. Have a look.

See also  Can A Light Be Too Bright For A Betta Fish?

1. It’s A New Tank

The first thing we suspect is a badly set-up new tank. If you are new to this hobby, we don’t blame you. It’s a tedious job to create an ideal betta tank. Being a freshwater fish, bettas are pretty sensitive about the water parameter. A slight increase/decrease in any parameter can cause huge stress to that poor thing. As a result, they choose to hide themselves.

It’s a survival tactic they even use in the wild. When the fish is sick or vulnerable for whatever reason, it chooses to stay away from other fish (be it a prey or a competitor). They don’t want to reveal their weakness or bad condition to the possible attackers.

Your new betta might be feeling uncomfortable around its strange tankmates. No matter whether the tankmates are friendly or not. Betta fish must ensure that predators or bullies do not surround it. That’s why bettas don’t come out during the daytime.

2. Doesn’t Like Its Hostile Tankmates

Bettas are not the friendliest fish in your tank. We can bet on that. Their instinct is to be super territorial. That’s the reason a male betta doesn’t like other male betta stepping into its area. You will find the two fighting almost every day.

Bettas accept fish that stay in a group and don’t fight with it. Siamese fighting fish like being the dominant one in the community. Another competitive fish in the tank means the two will have multiple combats. Once it is established that the other fish is physically stronger, Bettas are forced to surrender. But they don’t behave completely normal after that.

 Most of the time, bettas shut down their social life. They do their best to avoid the new leader of the tank. You will find them hiding behind a rock or sleeping during the day. Once the enemy falls asleep in the dark, that’s when Bettas chooses to come out.

We have sorted popular tank fish into two categories. Check out which fish get along with a betta and which don’t.

Sworn EnemiesRed tail sharks, Goldfish, angel fish, other male bettas, etc.
Most Friendly WithCory fish, cardinal tetras, Harlequin rasboras, Mollies, Neon tetras, Rummy nose tetras etc.

 Goldfish is quite bigger than a regular betta. So, they act like a bully most of the time. On the other hand, bigger shrimps make great tank mates for a betta. Shrimps don’t usually like to fight for territory. Considering a betta is much larger, the shrimp will easily give in and choose a peaceful life.

colorful betta fish in white substrate tank
Owner: Raven Persad

3. Light Is Too Bright

You were dreading this the whole time. sometimes, we like our aquarium to be the central piece of a room decoration. This leads us to attach lights that might be too bright for a betta’s eye. As a result, that poor thing only comes out when the lights are off.

See also  Do Betta Fish Need Light?

Bettas are able to see radiation far below the visible spectrum. They can see UV lights with a wavelength of around 10 nm (invisible to humans). So, if you use black lights in the aquarium, ensure it’s not too harsh. And, if the wavelength stays within the visible spectrum, you can easily measure its brightness level by yourself.

Here’s a rule of thumb. The aquarium doesn’t need more than 20 to 25 lumens per liter. If you have planted lots of grass or moss, the need for light will be a little higher. But stay away from bright white or natural sunlight. It can be too harsh for a betta’s eye. Especially because bettas are not bottom feeders. They love going to the top of the water surface and catching food.

As you know, the light intensity is much higher in that part of the tank. Since the fish can’t swim much while the lights are on, their sleeping pattern gets disturbed. They perform daytime tasks in the dark and try to sleep during the day. it can increase their stress level and bring out an aggressive temperament.

4. Betta Is Afraid Of You

Do you stare at your fish way too often? It’s a common trait of new betta-keepers. They just can’t get over their little fairy fish. But hey? Your fish might not like the idea of being watched all the time. They need a little privacy, too.

Believe it or not, bettas have different personalities. Some are friendly, while others tend to be more shy. Your bright shirt will distract them from their food. They might perceive you as a possible attacker. Hence, they choose to hide when you are in the room. Slowly, it becomes a pattern. Now, your betta only comes out when it’s dark.

It’s not a big issue. Avoid wearing too bright shirts or standing too close to the tank.

5. It’s Used To A Pre-set Rhythm

Have you bought a mature betta? Then, it’s possible that its previous owner set a different circadian rhythm for the fish. For example, some owners prefer keeping the light on throughout the night. And when they leave for work in the morning, they turn off the aquarium lights to let their pet sleep. The thing is bettas are highly dependent on this day & night time routine. Once it becomes a habit, you will have a hard time changing it.

You can contact the pet store or its previous owner. Ask them what was the betta’s sleeping cycle. If they confirm a different sleeping cycle, try to maintain the same routine. If the bettas love sleeping during the day, let them. Reduce or dim the lights to erase any kind of disturbance.

See also  How Much Light Do Betta Fish Need?- Dim Or Bright?

But if you want to change it, you must take one step daily. Start by reducing the water temperature (not too much, though). The range of 72 to 78 degrees Fahrenheit is considered ideal. So, use the cooler end of this range during the day. That will make the water slightly uncomfortable to sleep. The bettas will try to swim or eat, in an attempt to increase their body temperature.

As a result, they will get tired in the night. It’s your golden chance. Change the water temperature to how it was before. A tired and sleepy betta will snap out within a few minutes. Make sure you don’t provide food before bedtime. otherwise, they will get distracted by the pellets.

blue white gorgeous betta fish
Owner: Sean Aurellio

6. The Water Is Too Warm

It might sound weird at first. But yes, the problem can also be your tank’s water temperature. Most aquarists don’t check the water temperature daily. They install and set up a heater. That’s it.

Did you know that light can increase water temperature as well? Yes, it depends on what kind of light source you are using. LED bulbs don’t use heat as a medium for producing light. Meanwhile, incandescent or fluorescent bulbs do that. Almost 90% of the energy is transformed into heat. That’s similar to what natural sunlight does to your tank water.

The problem is, sunlight’s temperature can vary from day to day. During a cloudy day, the sun mightn’t interfere too much with the idea water temperature. However, wait till it is summer. The mid-day sunlight can even get humans sweating. Imagine your betta struggling inside the tank. It’s like you are slowly cooking it.

That’s why the poor fish chooses to stay hidden behind a plant or rock. Only when the lights are off does the water go back to the original temperature. Hence, the fish loves swimming when it’s dark.

Our suggestion would be to check the kind of lighting your aquarium has. If the light uses more than 20% of its energy to produce heat, remove them ASAP. LED lights are usually a nice option. Do you love the unique “yellowish” hue of halogen bulbs? Say no more. LED aquarium lights come in lots of colors as well. So, you don’t have to compromise in any way.

Before You Leave!!

Bettas need a sound cycle of light & darkness. That’s crucial for a betta’s mental and physical health. But don’t start putting your betta tank under direct sunlight. We have already mentioned why. But if you want to learn deeper, check out our article on “Is sunlight bad for betta fish.”

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Muntaseer Rahman

About Author

Hello, I’m Muntaseer Rahman, the owner of I’m passionate about aquarium pets like shrimps, snails, crabs, and crayfish. I’ve created this website to share my expertise and help you provide better care for these amazing pets.


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