What Does Blue Light In A Fish Tank Do?

Last Updated on 2023-08-08

Most likely, you’ve already done some work to make your fish tank look beautiful. Even if your fish tank is decked out in decorative rocks, driftwood, moss, and aquatic plants, and you still feel like something is missing, it’s because it actually lacks one more thing, and that is lighting. Lighting in aquariums and fish tanks not only makes them look nice, but it also affects how the fish and other animals grow. It can even change the way some fish act, which can be good if done in moderation. Read on to find out more about how lighting affects the fish in your tank.

What Does Blue Light In A Fish Tank Do?

As aquarists, we usually try to make our fish tanks look more beautiful and natural by adding driftwood, plants, algae, and even stones. Your fish tank will look even more stunning and realistic with the addition of blue light. Any color will do, but blue light has a unique effect on your aquarium inhabitants.

Aquarists have known for a long time that blue light calms fish because it looks like moonlight, which is what fish see in the wild. It also makes your tank look better by making the colors of the plants and fish stand out without making you strain your eyes. Blue light also helps plants grow, as it turns out that these shorter light waves have the most energy in the visible light spectrum. This makes them very important for photosynthesis and keeping the temperature of your fish tank stable since blue light doesn’t give off much heat.

Putting up blue lights has benefits that may seem too good to be true, but they are real. Blue light is, without a doubt, the best way to make your aquarium better for your fish and plants that live in water. Even better, this is the best way to make your tank look like a scene from the sea.

Is Blue Light Good For The Fish?

When adding something for looks to your fish tank, it’s a good rule of thumb to think about how it will affect the fish. Blue light also helps all the fish in the aquarium keep to their normal eating and sleeping times. Blue light is good for both the fish and the environment in the tank.

Blue light helps all the fish in the aquarium keep their eating and sleeping schedules in check. It can also make your aquatic plants healthier, which then releases more oxygen into the water and gives your fish a tank with a lot of oxygen. Lots of aquarists even use blue lighting to destress their fish, keeping them healthy. 

It’s a no-brainer that blue lighting in an aquarium is beneficial to the fish and other marine life there. Not only does it help your fish, but it also makes your aquarium look absolutely beautiful. Blue light has wonderful effects, but like most things, it’s best when used in moderation.

cerianthus under blue light in aquarium

Can Blue Light Harm Fish?

When we put something new into our fish tanks, we always make sure they are safe. Fish tanks are very delicate ecosystems that need the best care to avoid getting problems. There are some things you should know if you’re concerned that adding blue light to your fish tank will harm your fish.

Blue light could hurt your fish because it messes with their body clock and keeps them from sleeping, which can result in health problems. It was found in a 2019 study that goldfish exposed to blue light experienced increased retinal stress and visual impairments. There’s no doubt that blue light can hurt your fish in some ways. But the thing is, this only happens when blue light is used for very long periods of time.

On the contrary, it can have the opposite effect when used correctly. In addition to all the other good things it does, blue light has been shown to help certain fish’s growth rate by a lot. You might even find some aquarists that have been using blue light for years with no issues at all. Blue lighting can be a big help for your fish and aquatic plants, but only if you use it in moderation.

Is  Blue Light Good For Aquarium Plants?

There is no question that blue light is good for your fish. But whether or not blue light helps your water plants is a different thing. The aquatic plants you have can actually benefit from blue light, but there are some drawbacks.

Blue light is by far the most important part of the light spectrum for photosynthesis, so it is good for aquatic plants. Blue light makes plants’ leaves and stems strong and healthy. Also, blue light makes the colors of aquatic plants look better, which makes the fish tank look more colorful and rich.

Putting blue light in your aquarium, however, has another effect on plants. In the early stages of growth, when a plant is getting all of the light it needs, it has no reason to grow bigger leaves to get more light. Blue light also makes their leaves darker and may not have the best flowering. 

How Does Blue Light Affect Plant Growth?

Plants, both aquatic and terrestrial, benefit greatly from exposure to blue light. Aside from making your plants look better, it may also help their health and growth. While there are many upsides, there are also some drawbacks.

Plants need blue light to make chlorophyll, which is the most active pigment for photosynthesis. If a plant gets a lot of blue light, its stem and leaves will be strong, durable, and healthy. Blue light with a wavelength between 400 and 500 nm is used to help the stem and green leaves grow. 

 Blue light might really sound nice, and you might want to install one right away in your aquarium tank, but you should know that blue light discourages the plant from growing extensively. Plants grown with blue light tend to be shorter and have leaves that are small, thick, and dark green in color than plants grown without blue light because they get the light they need, so they don’t need to grow much bigger leaves.

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Blue Light VS White Light In Aquarium

Blue light can be a big help not only for your fish but also for the aquatic plants in your aquarium. But the same thing can also be said about white light. If you want to install lighting but aren’t sure which color you need, here are some differences between blue light and white light that you might need to know.

1. Feeding and Breeding

Blue light can make a place where fish want to eat and reproduce. It has been seen that blue light makes fish more active and makes them more likely to eat and mate than white light.

2. Growth

Blue light can be used to encourage growth better than white light. Blue light actually helps improve the fish’s metabolism, encouraging it to eat more.

3. Appearance of Fish

It has been seen that most fish look much better when they are in blue light. Not only does blue light bring out the blue color in your fish, but it also brings out the green and red colors. White light, however, is reflected by the fish’s scales very well and makes a soft shimmering effect.

4. Reduce Stress Levels

Blue light makes fish more active, which could keep them from getting enough sleep. White light, on the other hand, calms fish the most because it looks most like natural light, which makes fish less likely to be stressed.

5. Healthy Eggs and Larvae

There is still no proof that lighting affects the health of eggs or the growth of larvae. But there are studies that show white light helps the eggs and young fish of some species grow faster.

6. Aquatic Plant Growth

Photosynthesis needs blue light, but white light is better for plants. Plants need more than just blue light, which is found in white light. This helps them grow in a more balanced way.

7. Tank Appearance

Now, this opinion is subjective because it depends more on the taste of the aquarist. Blue light improves the lighting in a tank by giving it a blue color that looks like the ocean. White light, though, gives your fish a more natural look.


Can You Leave A Blue Light On In A Fish Tank?

A fish tank shouldn’t have blue light on for over 12 hours a day. In fact, no light should be turned on for over 12 hours a day in a fish tank. Every day, your tank should be dark for 12 to 16 hours to improve the health and growth of your fish, invertebrates, and even photosynthetic plants or corals.

Is Blue Light Good For Goldfish?

A 2019 study from the National Library Medicine found that exposing your goldfish to blue light for more than a week increased retinal stress and may have caused apoptosis in their retinas, even at a low intensity.

Does Blue Light Cause Algae In Fish Tanks?

Using only blue light to illuminate freshwater tanks will promote the growth of algae and cloud the water. Most algae thrive under blue light because it also benefits other aquatic plants.

Can Fish Sleep In Blue Light?

Since total darkness is necessary for fish to sleep, they will be unable to do so in a tank with blue lights on. Maintaining nighttime illumination will have long-term effects on their general well-being and behavior patterns.

Does Leaving Blue Light On In a Fish Tank Simulate Moonlight?

A blue aquarium light can simulate the moon’s glow. Blue light is commonly referred to as moonlight and gets its name from the way it illuminates the aquarium, inspiring movement among all the inhabitants.

Can You Use A Blue Light In A Tetra Fish Tank?

Blue light can be beneficial for all fish so long as it is used in moderation. The fish tank benefits more when it has aquarium plants in it.


Adding lighting to your already gorgeous fish tank will take its aesthetic value to the next level. Your aquarium’s fish and plants will reap many benefits from exposure to blue light. Your fish will be more active, and your plants will flourish. Just be careful not to expose your fish and plants to too much light, and avoid leaving the light on for too long, as it can be harmful to them. Like with anything else you put into your aquarium, moderation is key.

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