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

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.

You should turn off the aquarium light at night to facilitate a natural day and night cycle for fish. In general, most aquarium fish require 8-12 hours of light each day, with a recommended minimum of 8 hours of darkness to ensure proper well-being. Leaving the light on all night can lead to stress and algae problems.

I will delve more into this topic, and find out the benefits & disbenefits of lighting on fish. I’ll also recommend how you can automate your aquarium lighting, and keep your fish healthy.

Do Fish Need Light At Night?

Aquarium lights are on

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 In 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.

Let’s see what are some of the advantages of aquarium light.

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 on 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 also ensures that fish don’t lack oxygen and energy, crucial for their survival in the aquarium.

3) Helps To Darken The Fish Pigment

Research has shown that lights help 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.

Adverse Effects Of Light In The Aquarium At Night

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

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/light 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.

Aquarium light

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.

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. 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. Like humans, fish also have a circadian rhythm (a natural internal process that regulates the sleep cycle).

Prolonged exposure to light can affect their circadian rhythm, which may result in crankiness and fatigue.

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

How Long Should Aquarium Lights Be On

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 as I discussed above.

How Long Should Aquarium Lights Be On Ideally

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 plants and fish to get all vital nutrients from light.

That is why it is advisable to turn off the lights during the night and 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.

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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 difficult to regulate aquarium lighting on your own. Sometimes, you may forget to turn off the lighting at night before going to bed. Also, you can be away from home for some days.

Below are the ways that I recommend and I use to regulate lighting in your fish tank.

Method-1: Get A Timer

One of the best ways to regulate light in 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.

I have used this timer for a long time since I switched to the Finnex aquarium light that comes with a built-in timer.

Method-2: Aquarium Light With Built-In Timer

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 (what I actually do right now).

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.

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 betta fish & goldfish need light at night

Do Goldfish Need Light At Night?

Goldfish need 12/13 hours of light in every 24-hour 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?

While fish can technically live without light, providing them with a consistent light cycle is important for their overall health and well-being. Light is crucial for many biological processes in fish.

It includes regulating their circadian rhythms, supporting vision and coloration, and promoting growth and reproduction. Without proper light exposure, fish can become stressed, disoriented, and more susceptible to disease.

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. Use LED lights instead of incandescent or fluorescent lights because LEDs don’t produce heat like other lights.

Do Fish Sleep At Night?

Yes, fish sleep. 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.

Final Words

So, should you turn the fish tank light off at night? The answer is a big YES. You should turn off the light in your aquarium at night.

Switching off the light at night will help the fish get some sleep, which may help prevent them from losing their appetite and becoming lethargic or 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. So, turn the light off at night, don’t hesitate.

Aquarium Gears That I Use & I Recommend

I hope you find this article helpful, and got the answer you’re looking for. To make your aquarist life easier you can have a look at the products that I use for my aquarium. I am recommending them to you because I found them reliable, and worth every penny out of many.

  1. Aquarium light: A light can bring magic to the aquarium. It’s not just about brightening up the tank – it’s about syncing your fish’s daily rhythm. It’s highly beneficial if you’ve got a lush planted setup. I’m happy, I’ve stumbled upon a budget-friendly gem that’s perfect for plants. Curious? Catch the unboxing video here and see for yourself!
  2. Water conditioner: A water conditioner is another vital element in fishkeeping as it helps treat the tap water and makes it safe for aquarium use. I found Seachem Prime is the ultimate conditioner that removes Chlorine, Chloramine, and heavy metal readily from tap water. It also helps restore the slime coat in fish. Check it out here.
  3. Water test kit: Accurately measuring water parameters is crucial for fish tanks. You won’t know if anything goes wrong without testing the water parameters. Ever since I bought the API master test kit it makes my life much easier. You should have one, click here.
Sujit Modak

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