Do Fish Need Light at Night?

While we know that aquarium fish need light during the day, most aquarists have trouble deciding whether to keep the lights on at night.

But don’t worry, we’re here to help you out! The fact is most aquarium fish don’t need light in the nighttime. Because fish don’t close their eyes, you’ll have to dim or switch off the lights so they can sleep like they do in their natural habitat. Bright aquarium lights at night aren’t good for fish because they can stress them and lead to illnesses down the road.

To keep your aquarium pets happy, you need to make their fish tank as similar as possible to their natural habitat. So when nighttime comes, it needs to be dark, just like in their natural ecosystem.

Below are some tips that will help you decide on what to do with the aquarium lights in your fish tank.

How Long Should Aquarium Lights Be On? 

Aquarium lights should remain on for at least 8-10 hours during the day. Lighting in fish tanks is essential because it helps promote aquarium plants healthy growth and improves visibility when monitoring fish behavior. Coral reefs, fish colors, and the entire tank also look more attractive with proper lighting.

As vital as aquarium lighting is for fish and plants, they shouldn’t be on 24/7. Especially after feeding and when nightfall sets in, you should switch off aquarium lights to give your pet a chance to rest and sleep.

You can switch off the aquarium lights and turn them on in the morning to mimic the natural habitat of these fish. If you want to know why aquarium lights being on at night is so bad for your home aquarium, read below!

Reasons to Switch Off Aquarium Lights at Night

Here are some of the reasons why you should switch off the aquarium lights at night: 

1. So that your fish can sleep

Do fish sleep? The short answer is yes, of course. But did you know that fish don’t close their eyes when they sleep? As unusual as it sounds, most fish will sleep at night even when it looks like they aren’t, but they need the right environment.

Aquarium lights that are too bright will stress your fish, especially at night. They can’t sleep or relax if the lights are constantly on. That’s why you need to switch them off. You can do so when you go sleep or get aquarium lights with a timer. These light fixtures will automatically turn off at a specific time so you don’t have to worry about forgetting and putting your fish at risk.

Fish need to sleep to avoid getting stressed. Stress can lead to worse health strains for your fish, like fatigue, sickness, loss of appetite, and change in behavior. And no aquarists wants that.

2. To prevent algae overgrowth 

Algae in your home aquarium is good, but too much is dangerous to the habitat and other living creatures in the tank. Some fish species consider algae as a food source, but too much of it means you have to clean the tank more frequently.

One of the major causes of algae overgrowth is too much light in the tank ( even blue light) . While there are fish that can help clean the tank by eating some of the algae, it won’t be enough.

Lights at night will lead to an abnormally fast algae growth that will infect the entire tank. Too much algae can lead to the death of your aquarium plants because they compete for the same resources like nutrients and carbon dioxide in the fish tank. This messes with the tanks ecosystem. And when your fish don’t get enough oxygen from the water, they could die.

Algae overgrowth also tampers with the aesthetic of your home aquarium. And you don’t want your fish tank looking dirty because of the excess algae. You’ll even have a hard time spotting your little companions swimming in the fish tank.

3. To mimic your fish’s natural habitat 

The one thing you should do when taking care of a fish in your home aquarium is to keep them in an environment similar to their natural habitat. This helps them adjust to their new ecosystem much faster. Keeping the lights on during the day and turning them off at night will mimic the conditions they are used to in the wild.

4. Prevent overheating the tank’s water

The appropriate temperature in a fish tank should be as close as possible to the fish’s natural environment. Some freshwater fish need warmer temperatures than other species, so you need to know your fish’s needs. The last thing you want is to raise the tank’s water temperature so high that it affects your fish’s health and comfort.

Keeping the lights on at night can increase the tank’s water temperatures because most light fixtures tend to generate some amount of heat. This is especially true if you’re keeping fish in a small aquarium. Your fish might not be affected if they are in a larger tank with more water, but it’s best not to risk it.

5. To prevent slow plant growth 

Plants, Like most living creatures, need sunlight to thrive. Light is essential for plants to carry out photosynthesis which also helps increase the amount of oxygen in the tank’s water for your aquarium fish.

Plants only need a couple of hours of sunlight to grow healthy. Overexposure to sunlight or artificial lights isn’t helpful to the healthy growth of your plants . Giving plants a similar day and night cycle in the tank is recommended to prevent them from dying.

When Do Fish Need Light at Night? 

Most of the time, fish don’t need light at night. But in their natural habitat, many fish are exposed to moonlight. So a little light won’t hurt. Below are some of the instances when fish need aquarium night lights:

1. When breeding

Breeding is a special time for fish; they need constant supervision to prevent anything from going wrong. Most fish depend on moonlight to synch their biological rhythms. So adding dim lights to their aquarium can actually help when they are spawning. A lot of things can happen at night when your fish are breeding.

Hence the best way to keep up with breeding fish is by adding a night light. Tropical fish like guppies will lay eggs towards dawn, and you don’t want to miss this beautiful process.

Some fish lay eggs at night, and you need to keep an eye on them in case one of the older fish decides to eat them. . If the tank isn’t in an area with direct moonlight, artificial lights like blue light could be the best alternative.

2. When they are sick 

Most fish species are prone to sickness, so you need to keep an eye on them to ensure their illness doesn’t worsen. Monitoring their behaviour is also important to understand what’s wrong with them and better help them heal.

Some fish species are also comforted by dim lights, that can help them stay at ease as they recover from their illness.

3. If your aquarium fish are nocturnal 

Are your fish nocturnal? If you’re keeping fish that sleep during the day and are awake at night, then they will need additional light at night. They can comfortably swim in the dark, but seeing them out and about is interesting for most fish keepers.

Aquarium lighting will also be helpful when feeding these fish. Fish species like knife fish are shy and don’t want to fight for their food, so they’ll wait until later in the day to eat. If you want your nocturnal fish to be more comfortable at night, you can add light fixtures if their environment doesn’t provide as much light as they need. It will also be easier for them to see their live food and for you to monitor their feeding habits.

Some nocturnal fish species misbehave towards fish that are active during the day(diurnal fish). Using aquarium lights can help it find out if these fish are getting along or causing trouble with their tank mates.

Nocturnal fish like the blue botia and large plecos have a reputation for of bothering sleeping diurnal fish. If you have these species in your community tank, you’ll need a night light.

What About Colored Lights? 

Although some aquarists prefer using blue light for their fish at night, your fish don’t mind which color it is. The color you choose will mainly be for aesthetic purposes or more specific if you have a planted aquarium.

Blue light doesn’t adversely affect aquarium plants or a fish’s sleeping pattern or promote algae growth. If your home aquarium’s location isn’t in an area with natural light, blue lighting can be the best alternative. Even better than other light fixture options asinin available for fish tanks.

It also doesn’t affect tank inhabitants as much as direct sunlight and LED lights, but your fish may be unable to tell the difference. While blue light isn’t as harsh for fish because it is similar to moonlight, it can still prevent some fish species from sleeping.

Be careful because a very bright night light can still cause harm to your fish. Dim lighting is more natural and closer to moonlight if you plan on adding to your home aquarium .


Most fish don’t need light at night. Unless they are breeding, sick or nocturnal. Otherwise, they prefer the darkness so they can unwind from a long day of swimming and get some rest. Constant light can quickly contribute to stress and aggressive behavior in your fish.

Once your fish is used to a specific lighting schedule, it’s best not to disrupt it. The best option is to get lights for your fish tank with a timer, so you don’t forget to turn them off at night. This is similar to their natural habitat and will help keep them comfortable in your home aquarium.

If you want to keep an eye on your pets, you can choose a dim light that won’t affect your fishs sleeping pattern.


Do betta fish need light at night? 

No. Betta fish don’t need light at night. They aren’t nocturnal, so you can switch off the lights at night to let them relax and sleep.

Can aquarium lights be too bright? 

Yes. And too bright lights can affect your fish’s mood and health. The best option is to get aquarium lights with controls so you can dim them when necessary.

Do saltwater fish need light at night?

No. Saltwater fish need a regular light cycle to sleep at night. This is similar to what they experience in their natural environment.

Do fish need total darkness to sleep? 

Most fish will appreciate no lights in their tank when they want to sleep. It doesn’t have to be complete darkness, but low to dim lighting will help.

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