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Should I Turn My Fish Tank Light off at Night? Find the Fact

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  • September 27, 2020May 27, 2022
Should I Turn My Fish Tank Light off at Night by Aquarium Tales

Should I turn my fish tank light off at night? This is a popular question asked by many aquarists. There is a controversy about this topic. 

Some aquarists support turning off the lights at night while others keep leaving them on an entire night. As a result, most people are confused about which option to choose. 

If you have just bought a fish tank and wonder whether you should turn off the fish tank light at night, then today, you are in the right place. I will delve more into this topic and recommend the best practice that I do for my tanks. Keep reading. 

Do Fish Need Light At Night?

Aquarium plants need light for photosynthesis, but fish don’t have any biological need for light. Except pigmentation of some species of fish accelerates by light. Light allows them to sight for regular activities like movement, taking food, etc. Fish don’t get light at night in the wild. So, staying in the dark at night is natural for them.

Additional light in the fish tank is a crucial consideration when you have plants in it. Because plants need adequate light to flourish. In a planted tank, you’ll have to identify a balance point of light and darkness, which will be ideal for all tank inhabitants.

Benefits Of Light At Night In The Aquarium

Lighting in the aquarium is essential. An aquarium is a feature piece that enhances the beauty of your place. Lighting is a must-needed part of decorating the aquarium.

Light is crucial for plant growth in a planted tank. The intensity and duration of lighting in such aquariums depend upon the requirement of plants. Reef tanks need special lighting with a complete spectrum suitable for coral growth.

So, if you keep the light on at night, will it give any benefit? Yes, it will. Let’s see what those are.

Benefits of Light at Night in the Aquarium

1) Enhances Visibility In The Aquarium

Light helps to enhance visibility in the aquarium, thus allowing you to see what is going inside. It will enable you to see the beautiful colors of your fish, how they interact with each other, their behavior, the aquarium’s cleanliness, and the plant color in the aquarium. In other words, good lighting at night gives life to the aquarium.

2) Provides Energy And Oxygen In The Aquarium

Lighting also provides oxygen and energy in the aquarium, enhancing the fish’s well-being and the proper growth of photosynthetic plants and organisms.

Most plants have a photocycle of around 12 hours. This means that they need light for about 12 hours a day to thrive. Proper lighting at night also ensures that fish don’t lack oxygen and energy, crucial for their survival in the aquarium.

3) Helps To Darken The Fish Pigment

Lighting at night is also beneficial to the fish. Research has shown that lighting at night helps speed up the darkening process of fish pigmentation, allowing them to reach their full-color potential fast.

This is important as it helps to give the aquarium an attractive and vibrant look. Some fish can also become lethargic, lose their appetite, and eventually die if there is no proper lighting in the aquarium at night.

Adverse Effects Of Light In The Aquarium At Night

Even though lighting at night in the aquarium is somewhat beneficial, it also has its harmful effects. Below are the negative effects of turning on the light in the aquarium at night.

negative effects of aquarium light at night

1) Affects Plant Growth

There is no doubt that aquarium plants need light to thrive. Photosynthesis (the process in which plants combine water and carbon dioxide to produce food) can only occur in the presence of light.

However, most plants only need 12 hours of sun exposure to make their own food. Overexposure to light will negatively affect plants in the tank because they also need darkness (for at least 12 hours) to respire.

Even in the natural environment, plants are exposed to light for 12 hours and darkness for another 12 hours. Overexposure to light can create free radicals in plants, generating reactive oxygen species that may destroy the plant.

2) Leads To Algae Overgrowth

Another adverse effect of lighting your aquarium at night is that it leads to an algae bloom. Algae thrive when exposed to light. The more lights they are exposed to ( natural or artificial), the faster they grow and multiply.

Green algae photosynthesize just like plants. The only difference between them is that green algae can make food through photosynthesis for 24 hours, leading to the overgrowth of algae in the aquarium. This can negatively affect the aquarium ecosystem.

When there is a high algae population in the aquarium, they will compete for precious resources such as carbon dioxide with the plants. Because they are more aggressive, their dominance will lead to plants dying off in the aquarium.

Some fish love feeding on algae. However, not all algae are consumed by fish. For instance, green algae are not consumed by fish, meaning that their growth in the tank cannot be controlled. The Algae bloom can affect the health of fish and plants in the aquarium.

It also makes the tank look dirty. One of the best ways to regulate algae growth is by switching off the light in the tank at night. This way, they will not get the much-needed energy to thrive.

3) Affects Fish Health And Well Being

Overexposure to light (natural or artificial) can affect fish health and well-being. Research has shown that particular fish species like goldfish become lethargic and lose appetite or become ill when exposed to light for an extended period.

Over time, such fish may die. Some fish become very aggressive or sleepless when exposed to long hours of light. The only way to prevent this is by switching off lights at night to give the fish time to sleep.

Like humans, fish also have a circadian rhythm (a natural internal process that regulates the sleep-wake cycle). Prolonged exposure to light can affect their circadian rhythm, which may result in crankiness and fatigue.

If you don’t turn off the light at night, fish will not differentiate between day and night. This may affect their circadian rhythm, and they may become passive or aggressive.

Recent research also suggests that artificial light, especially during the night, may affect fish visibility. Many fish species are affected by prolonged exposure to light. Excessive light causes stress, which may trigger aggression leading to fights in the tank, some of which can be fatal.

How Long Should Aquarium Lights Be On

How Long Should Aquarium Lights Be On Ideally

A common error and misconception that most aquarists make are keeping the aquarium lights on for 24 hours. Keeping the light on the aquarium for 24 hours is not recommended. It is not only a waste of electricity, but it can significantly damage the health and well-being of your fish and plants.

Both fish and plants need a period of sunlight and darkness to thrive. They are living organisms and operate on cycles, just like humans. Overexposure to light will negatively affect your aquarium ecosystem and may lead to fish and plant death.

The length of time in which you need to turn off the aquarium light is debatable. However, most experts recommend that you provide 12 hours of light and 12 hours of darkness.

Numerous scientific studies have also revealed that 12 hours of light exposure is sufficient for the plant and fish to get all vital nutrients from light.

It would help if you kept all aquarium conditions as natural as possible by tuning the lights On and Off in a predictable manner. That is why it is advisable to turn off the lights during the night for 12 hours then turn them on during the day when it is beneficial to both the plants and fish.

Turning off the light at night will also help regulate the growth of algae in the fish tank.

How To Regulate Lighting In The Aquarium

Consistent lighting in the aquarium is crucial. Fish and plants have their own cycle, and you need to ensure that they are not disrupted by keeping the aquarium’s lighting conditions as natural as possible.

However, it is impossible to regulate aquarium lighting on your own. Sometimes, you may forget to turn on the lighting in the morning before going to work, and sometimes you can be away from home for some days. Below are ways to regulate lighting on your fish tank.

Method-1: Get A Separate Timer/Aquarium Light With Built-In Timer

One of the best ways to regulate light on your fish tank is using a timer. A timer is a device that automatically turns the aquarium’s light based on your settings. For instance, if you set the timer to turn the light on/off after every 12 hours, the timer will execute that command accurately.

In addition to regulating lighting in the tank, the timer also helps control the light intensity by increasing or decreasing light intensity based on your settings.

A timer is a crucial device that may help eliminate the stress of worrying about your fish tank lighting all the time. You only need to set it up, and it will do the rest, thus maintaining a healthy life for the plants and fish in the aquarium.

Nowadays, technology is advanced, and you don’t need to buy a separate timer to regulate your aquarium light. Instead, you can use aquarium lights with built-in timers with day/night cycles.

I use Finnex Planted+ 24/7 CRV light for my 30-gallon aquarium, which I found beneficial for plants and fish color. Most importantly, a built-in timer allows me to mimic day and night in my aquarium with ease.

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Method-2: Apply Ambient Blue Light

If you prefer your fish tank to have light all the time, then you should use ambient blue light. This light doesn’t in any way affect the day and night cycle of plants and fish in the aquarium.

Additionally, they also don’t contribute to the growth of algae. This light is highly recommended for aquarists who want to improve the fish tank brightness without affecting fish and plants’ health and well-being. Blue ambient light produces illumination with a low intensity that does not affect the aquarium ecosystem.

Method-3: Use Headlights

Some aquarists may use headlights to regulate the temperature in the aquarium. However, if you use a headlight to control your aquarium lighting, ensure that you don’t choose bright headlights. Because they may affect fish visibility, thus affecting their feeding habits. The headlight should also not alter the optimum temperature in the fish tank.

Do Betta Fish Need Light At Night?

No, Betta fish don’t need additional light at night. In fact, extended lightning periods can be bad for their health. Like all other living beings, Betta fish need rest and sleep. The darkness of the night is their resting time.

Betta is a tropical fish native to Vietnam, Cambodia, Laos, and Thailand. In those regions, the average duration of daylight is 12 hours, extended to 15 hours during the summer.

It is better to mimic the natural environment in the aquarium. So a 14 hours lighting period is an ideal duration for Betta fish.

Do Goldfish Need Light At Night?

Goldfish need 12/13 hours of light in every 24 hours cycle. So they don’t require additional lighting at night. Instead, they need darkness for rest.

Though adequate lighting is essential for them to maintain a glowing color. If kept in darkness, goldfish start losing bright body color. Full-spectrum color provides vitamin D, which is vital to keep goldfish looking attractive.

So, I’ll suggest adequate lighting for 12 hours for your goldfish. Then, the rest of the time, allow them to stay in darkness.


Can Fish Live Without Light?

Yes, some fish can survive without light. Some saltwater fish that live deep in the ocean don’t require light to survive. 

However, most tank fish require light (a minimum of eight hours and a maximum of 12 hours) to survive and thrive. Just like humans, fish have biological needs and require light to thrive in the aquarium.

Are Artificial Lights Bad For Fish?

No, artificial lights are not bad for fish. However, the lights should not be too bright or cause fluctuation in the fish tank. However, the type of light that you choose for your aquarium is very important. 

LED lights are much better in fish tanks than incandescent and fluorescent lights because they don’t produce a lot of heat that may cause fluctuation in water temperature, which may harm some types of fish.

Do Fish Sleep At Night?

One of the reasons you should turn the light off at night in the fish tank is to give the fish ample time to sleep. But do fish really sleep? Yes, fish sleep. Like humans, fish usually sleep at night but don’t close their eyes because they don’t have eyelids.

Therefore it isn’t easy to know whether they are sleeping or not because their eyes never close. Fish can seep both during the day and night, but they mostly sleep during the night when it is dark and quiet. When they are asleep, their body movement is slow. Most fish also like hiding when taking a nap.

Are Colored Lights Bad For Fish?

Colored lights don’t do anything terrible directly to fish, but color-changing lights can impose stress on them. 

I have observed a bit of restlessness among my aquarium fish when I set sequential color-changing mode. Actually, this is not the effect of colored light, but they become scared by the change.

Also, you need to be careful about heat release caused by aquarium lights. LED lights don’t produce heat, but incandescent lights can cause heat issues. Fluctuation in temperature caused by color lights can be harmful to fish.

Can A Light Be Too Bright For Fish?

Fish are not as light-reliant as aquarium plants are. Still, it is better to mimic a natural environment in the aquarium to create a healthy environment. Too bright light can stress fish and make them uncomfortable.

It can cause overheating of the water as well. Therefore, it is better to avoid too bright lighting for fish unless it is a heavily planted tank.

The lighting requirement is high in a densely planted tank, but it will not affect the fish adversely as they will get plenty of shadow and hiding places there.

Final Words

So, Should I Turn My Fish Light Tank Off At Night? The answer is a big YES. You should turn off the light in your aquarium at night. Most fish require a period of light and darkness each day to thrive. 

Therefore, turning off the lights in the fish tank is an excellent idea because it mimics the natural cycle of day and night, which is vital for fish’s well-being.

Switching off the light at night will help the fish get some sleep, which may help prevent them from losing appetite and becoming lethargic and aggressive. 

Plants also need light during the day to make food but don’t need it at night. So, turning off the aquarium light at night will also benefit the plants.

Algae growth, a big problem in fish tanks, is best controlled by turning off the fish tank light at night. Algae thrive on light exposure, meaning that the more you expose them to light, the faster they grow and multiply. So the best way to limit their growth is by turning the lights off in the aquarium at night.

If you don’t want to turn the light in the aquarium entirely off, you should use ambient blue light because it doesn’t affect fish and plants’ general well-being. They also don’t promote the growth of algae.

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