Betta fish and blue light: Why not only sunlight?

Oftentimes when setting up an aquarium for our betta we ponder whether or not to add artificial light to your tank or if just sunlight is enough to meet their needs.

In this post, we are going to discuss whether sunlight is sufficient for your betta, what is blue light, why some aquarists use blue light in their betta tank. We will also talk about whether blue light might be harmful to your betta or not.

Betta fish and blue light: Why not only sunlight?

Some people rely only on sunlight for their betta tank. But no, only sunlight is not good enough for your betta’s needs. The issue with relying only on sunlight is that you do not offer a controlled environment to your betta. 

There is no guarantee that your betta will receive the same amount of sunlight every day. Also, too much sunlight can cause an algae bloom. An algae bloom reduces the plants in your tank to receive proper sunlight. Algae will also compete with them for CO2 so they can use it during photosynthesis. Moreover, it can also affect your bettas by facilitating them to get bacterial infections like fin rot, dropsy, columnaris, and Popeye.

An additional problem that may happen relates to how sunlight affects the temperature. If your tank receives sunlight for most of the day, the temperature in your betta’s tank will increase to a point that might leave your fish extremely uncomfortable and in the worst-case scenario, it can lead to death.

Using blue light

Unlike sunlight, artificial lights do not affect your fish tank’s temperature. Hence, the chances of having algae bloom in your tank are reduced. Besides, there are automatic lights that you can program to turn on and off during specific times. So, you do not need to worry about forgetting to turn your betta fish light on or off at night.

What Is Blue Light?

The light spectrum is composed of seven colors. When all colors are present in the same place we call it white light, which is similar to daylight. Blue light is a high-energy light provided only by one color of the spectrum. Plants benefit from blue light, as it provides them energy for the photosynthetic process. 

What type of lights can I use in a tank? 

There are 3 types of light you can use in your betta aquarium:

  • Fluorescent lights;
  • LED lights;
  • Metal Halide light.

Fluorescent Lights

Fluorescent light is the most common type of fish tank lighting. The light comes in a single unit with 4 to 6 tubes and you can change the color of the light by selecting the tubes you would like to use. Most aquarists choose blue, red, and white fluorescent tubes to use in their tank.

LED lights

Light Emitting Diode lights, more commonly known as LED lights, are frequently employed in aquariums that use carbon dioxide injections to combat algae bloom. They are powerful and long-lasting lights.

Metal Halide Light

Metal halide light is a high-intensity light, which can be costly to maintain due to the high price of the light bulbs. However, the overall running costs of such light are low. One thing to consider before buying metal halide lights for your tank is that they use mercury gas. So, make sure that they are set up properly to avoid harming your betta.

Important things to consider when using artificial light in your betta tank

When adding a light to your tank you should aim for about 1.0 watt per gallon for LED lights. If you choose fluorescent lights, 1.5 to 3.0 watts per gallon will suffice. If you are in doubt, you can ask a professional at your local pet store the best light you can buy for your tank setup.

Once you have installed the artificial light in your tank, monitor it for a while. Artificial light can make your tank reflect in on itself, which can make your betta may think that its territory is being threatened. Consequently, the fish attacks its reflection. 

To avoid such a thing, you can either buy a weaker light or make the reflection stop occurring. You can lower the chances of reflection by turning your tank light on at the same time the room’s light, where the tank is located, is on. Your betta is most likely to see himself when your tank light is on but the room light is off.

You can introduce the blue light to your betta little by little. Start by turning the light on for a couple of hours a day. You can gradually increase it until there is no display of aggressiveness and you reach the necessary time for the betta’s light cycle. Also, place aquarium paper on the exterior part of your tank (lateral and back parts) to make it look darker.

Do bettas need blue light?

Fish do not necessarily need light. However, they need a day-to-night cycle. Tank lights can mimic this cycle besides providing a constant amount of light without increasing the water temperature by a whole lot.

Some people have the misbelief that blue light is to be used to make fish sleep. Fish do not sleep like mammals. They reduce their activity and metabolism when they rest, albeit remaining alert to their surroundings. These periods where the fish is “asleep” may have the same restorative effects as sleeping does to mammals.

How long must the light-dark cycle of a betta last?

When setting up an aquarium for fish or other creatures, we must mimic their natural environment the best we can, guaranteeing a good quality of life for them. Bettas often have shorter days as the vegetation present in their natural habitat may block the sunlight to reach the whole water column.

Hence, a light cycle ranging from 8 to 12 hours a day is enough to meet your betta’s requirements. So, remember: you can choose an 8 hours light and 16 hours dark cycle or a 12 hours light and 12 hours dark cycle. 

A balanced light-dark cycle prevents your betta from getting stressed or having a weak immune system. You can find the best time to set your light up according to your betta’s activities. If your betta is diurnal, that means it is more active during the day. If nocturnal, it will be more active during nighttime. This way you will know when to turn on and off your light. And do not worry about forgetting to turn the light on or off. There are light systems with timers so you can program the chosen light-dark cycle to your betta.

Is blue light harmful to bettas?

Blue light is commonly used in aquariums to set the day-night cycle for the betta but also so aquarists can get a clearer view of the tank. There are studies about the effects of blue light on fish. Blue light can have different effects on fish, depending on their species. So, it is not one size fits all.

While a study says that blue light can affect the eyesight in Goldfish, another states that it may reduce the stress level in Nile tilapias. Thus, you must respect the light-dark cycle of your betta by not exposing it to more than 12 hours of light, and monitoring its reaction towards this light. If your betta gets too shy or if its appetite is influenced when the blue light is on, you can always change the light.

Will plants benefit from blue light? How about algae bloom?

Yes, plants and algae benefit from blue light. However, you must keep an eye on microalgal growth to avoid an algae bloom.

Photosynthesis is performed by both plants and algae. During this process, the pigment that gives plants and algae the green color known as chlorophyll captures the light and reacts with a carbon source (CO2) producing sugars. This process allowed plants and algae to thrive in the most different environments around our planet.

Chlorophyll absorbs blue (short wavelength) and red (long wavelengths) well. But it does not absorb the middle wavelengths of visible light as effectively, whereas ultraviolet light can be damaging to plants. The same can be said for algae. Bettas enjoy having plants in their tank for hiding, resting, and even nesting purposes. But algae bloom in a betta tank is not good for it.

A good filtering system with low current and regular cleaning can solve the problem with algal growth. You can also add organisms that feed on algae, like red cherry shrimps, nerites snails, and some bottom feeders, if your betta’s temperament allows it to have tank mates. 


In this post, we have discussed betta fish and blue light. We explained that sunlight may not be beneficial to bettas because besides not giving the fish a reliable and controlled amount of light if the tank receives a strong and direct light, the betta can get stressed by the increase of the water temperature and can even die from it. Thus, artificial light is recommended. 

We also mentioned the different types of lights (fluorescent, LED, and metal halide) and what to expect when adding blue light to your tank. If you notice your betta is displaying signs of aggression after you have turned on the blue light, then it could be due to the fact that he is seeing his reflection. 

The betta will feel threatened and attack its reflection on the glass. You can try to stop this behavior by removing the light for a while, increasingly adjusting the time your light is on so your fish can get accustomed to the light, or even putting aquarium paper in your tank to make it darker. 

Bettas, like any other fish, need a constant light-dark cycle to rest. Blue lights can be good for betta fish as it mimics the transition between day and night. Aim to give an 8:16 or a 12:12 hours light and dark cycle. Anything above 12 hours of light can be detrimental to your betta’s health and ability to rest.

There is no consensus on whether blue light might be harmful to your fish. Different studies obtained positive and negative results depending on the species. Thus, there isn’t one final answer regarding the use of blue light.

Finally, plants benefit from blue light as much as algae. To avoid an algae bloom, a proper filtration system must be installed in the tank with low current and regular cleaning as well. You can also try to add tank mates that feed on algae if your betta allows it.

Blue light can be beneficial to your betta. Does your betta tank have blue light? Does your betta enjoy blue light? Let us know your experience by leaving us a comment below.


Song, J.A.; Choi, C. Y. (2019). Effects of blue light spectra on retinal stress and damage in goldfish (Carassius auratus). Fish Physiol Biochem, 45:391–400.

Volpato, G. L.; Barreto, R. E. (2001). Environmental blue light prevents stress in the fish Nile tilapia. Brazilian Journal of Medical and Biological Research, 34: 1041-1045.