Should I Turn My Fish Tank Light Off At Night?

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Lighting helps an aquarist observe their fish better. Most importantly, it helps maintain a healthy sleep-wake cycle in the aquatic ecosystem. But for several reasons, some pet keepers are often found posing this question-“Should I turn my fish tank light off at night?

Some aquarists prefer to keep the lights of their aquarium off at night because they like to see their tanks all lit up in the morning. Pet keepers who stay busy most of the time during the day, prefer to keep the lights on at night so that they can see their fish buddies better and make a stronger bond with them.

If your house stays brightly lit up most of the time, then you can definitely opt for the option of keeping the lights off in the fish tank. But keeping the tank near open windows during the daytime, with the lights of the aquarium on at the same time, is not a good idea.

Excessive exposure to light might prove to be harmful to your fish in more than one way you can imagine. So should you turn the lights off at night? Let’s solve your dilemma.

Pros Of Light: Why Do Fish Need Light?

Consider a fish’s natural habitat. In nature, there are 12 hours of light and 12 hours of darkness. Fish are used to such regular cycles and they also like it.

When we bring a fish home and transfer it to its new house called an aquarium, the fish do expect the same cycle to continue. Therefore it is highly advisable, that you provide your fish in your home fish tank equal hours of light and darkness.

Certain fish like the goldfish may lose their vibrant coloring in the absence of light. Some fish might become lethargic and lose their appetite if light exposures are inadequate.

Studies have shown that longer exposures to light will brighten up the colors of many species of fish because the light helps in the production of their body pigments.

Plants, needless to mention, depend on light, especially sunlight, for photosynthesis.

It is a process in which plants combine carbon dioxide and water to produce their food, and the process needs a pigment called chlorophyll which gives the plants their green color. Most plants need 12 hours of light exposure for sufficient photosynthetic activities.

Should I turn my fish tank off at night?

1. Algae Bloom

Unless you want your fish tank to be smothered with the greenness of algae, you would want to keep your tank away from a light overdose. Excess hours of light, be it natural or artificial lighting, may lead to algae bloom or algae overgrowth.

Green algae do photosynthesis just like plants do. When the algae population has flourished in the tank, they will compete for the resources with the plants, and this competition may prove to be quite aggressive for the plants.

You might find that your aquarium plants are dying off due to excess algae. There are multiple ways of getting rid of the algae for sure—certain shrimps and fish love feeding on them.

But what if the blue-green variety, which is not even algae to begin with (they are bacteria), infest your tank? Most fish decide not to even go near them. In that case, you might have to go through rigorous water changing and water treatment regimes, which is a lot of work and will cost you big time.

2. Effect On Plants

Overexposure to light does not always mean that plants will thrive. Even in natural environments, when it is nighttime, plants do not photosynthesize. Instead, they respire, just like animals.

This is what they are accustomed to. They thrive the best when given 12 hours of darkness, along with 12 hours of light.

3. Effect On Fish

When exposed to long hours of light, be it artificial or natural, certain fish become sleepless or aggressive. Some fish are diurnal, meaning they thrive during the day. Others are nocturnal, which means they are nighttime creatures.

Compare this to the circadian rhythm of humans which helps regulate our sleep and wake routines. Keeping awake in the late hours and waking up late the next day, and maintaining this routine for months, will disrupt the circadian rhythm majorly.

This disruption is enough to cause fatigue and crankiness, and other such worsening health symptoms, in humans. The same can happen to your fish.

Should I turn my fish tank light off at night? The debate is not over yet but don’t be surprised if your fish act lethargic one day, or are found to be restless and aggressive with their play mates. Some species of fish find darkness as the “resting time” and that is when they feel calmer, and are more relaxed.

By exposing them to too much light for long hours, you are actually robbing off the “me” time from your fish’s life. Some fish might even stop eating when all they see is light around them.

4. CO2 Treatment

If you maintain a large high-tech tank, you might need to opt for CO2 injections which add the gas directly into the water columns so that your photosynthesizing plants can utilize it. This gas diffusing into the water columns will run out faster if you keep your fish tank lights switched on 24/7.

How Will I Regulate The Lighting In My Fish Tank?

1. Timer

A timer, also known as an automatic dimmer, will help you do that. Setting a fixed time on this timer will switch the lights of the fish tank off at that particular time.

Automatic dimmers can be set to regulate the intensity of the lightings in your fish tank—a well-regulated dimmer will increase or decrease the brightness of the aquarium lightings at fixed times of day or night. You can also set a “wake up” time when the timer will automatically turn all lights back on.

This regular cycle of light and darkness will help maintain a healthy life for the fish and plants in the aquarium. It will mimic the natural environment which the living organisms are habituated to, and will reduce stress in some fish species.

Should I turn my fish tank light off at night? Your timer can do that for you. Setting up dimmers and timers to an 8-hour circle will do enormous good to your fish and plants.

Maintaining a regular light-dark cycle in your tank will make your fish get used to it. Thus you are nurturing a healthy rest and playtime for your fish.

An observation by an aquarist on his rummy nose tetra fish is an interesting example. After having established a good dark-light cycle in his aquarium, he noticed that when he turns the lights on at night, the noses of the fish are not red.

But when the lights turn on at the same time as set in the timer, the fish’s nose turns red or more colored than usual. This shows fish’s physical response to the light-darkness cycles and proves that fish do get affected by this practice.

2. Heat Lights

If you use heat light to provide warmer living conditions to your tropical aquarium fish, then make sure they are not the bright ones. You can consider the option of using ceramic bulbs in your aquarium which produce only heat, and not light. Ceramic bulbs are readily available in any pet store or online.

3. Moonlight

You may prefer lights on all the time because let’s face it, lights let you keep an eye on your fish and the interiors of the tank to spot anything abnormal. One thing you can do is add moonlights to our tank, which produces a brightness of low intensity.

As the name suggests, moonlights emit blue light that creates a blue ambiance inside your aquarium. Not only do these lights add a mystified effect to your tank, but they do not have any side effects.

They neither promote algae growth nor affect the sleep-wake cycle of your fish. You can also consider LED lights, which produce only light but no heat, and are available in different colors.

4. Seasonal Variations

In winter, you can expose your tank to longer hours of high-intensity light. It is because in winter, natural light is less, and also the temperatures are low.

A Conclusion To The Debate

Should I turn my fish tank light off at night? Yes, you can, depending on how many hours were the lights on or off the rest of the day. Fish, in particular, do not need lights at night. Plants complete their photosynthesis during the daytime and respire at night without the need for light to be present.

So if you find that you have kept the lights on for a total of 12 hours in the daytime, you can surely go for lights off for your tanks at night. Alternatively, you can set timers or dimmers which will make sure that your tank organisms get 12 hours of light and darkness in chunks all throughout the day.

If you do not want to keep your tank lights off completely, you can opt for the dimly glowing moonlights or automatic dimmers.

Any procedure you choose to use, just make sure that your aquarium is exposed to 8-12 hours of light and 8-12 hours of darkness every day.


Q.1) Do fish sleep at night?

Ans: Yes they do sleep and like to rest for a while. We cannot detect that they are sleeping because they do not have eye-lids. So even if they sleeping, their eyes remain open.

Fish sleep, when they need to, even when the lights are on. But when they are sleeping, their body movement slows down and they stay still for a considerable length of time. The only movement you might observe would be in the gills and mouth area.

Also at night, if you try to observe them in dim lights, you might see them all flocking in a corner or at the bottom of the tank, close to the substrate, probably stealing a quick nap or catching up on daily gossip!

Q.2) Is light harmful for goldfish?

Ans: UV light from sunlight is both beneficial and harmful for goldfish. While the fish may use UV light to regulate their daily wake-activity-sleep cycle, excess of UV may harm the fish.

Goldfish get their vibrant colors from a pigment the production of which is connected with the amount of UV it is exposed to. A lot of light, high in UV, will make goldfish appear more bright, while low light intensity may cause the fish to appear paler.

Should I turn my fish tank light off at night? Some hours of darkness will benefit the goldfish. Prolonged exposures to UV light may damage the fish’s retina and the embryo of expectant mother goldfish. In conclusion, the right dose of light will benefit the goldfish, not cause it harm.

Q.3) Which plants require more light or less light?

Ans: Plants that have red-colored segments in their leaves or stems, require more hours of high-intensity light. Tropical plants like water ferns, java, banana and amazon will thrive in regular 12 hours of light. Cold water plant species like Anubias or tiger lotus thrive better in seasonal light variations.

Q.4) What kinds of fish need light, and which ones don’t?

Ans: Fish like tetras and cichlids need less light. Tropical fish need 10-12 hours of light. Cold water fish or temperate zonal species, examples include goldfish, ricefish, minnows, and zebra fish, thrive best in seasonal variations of light intensities.

Final Word

Lighting is quite necessary to note fish and plant growth. It is also essential to keep track of their health and mitigate any infestation by unwanted organisms.

But keeping the lights on for long hours will create a havoc which your had not expected. You wanted peace for yourself by looking at the tank and enjoying fish movements. Instead it has turned into this snarling, nerve-wracking tank of aggressive fish which had been the last of your expectations.

Should I turn my fish tank light off at night? Yes, you can. Just ensure that your aquarium is being exposed to 8-12 hours of light all throughout the day. Timer and dimmers will help you a lot regarding this.

Any more questions? Feel free to drop them at the inquiry box and we will get back to you with information that you can rely on.

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