Do Aquarium Fish Need Lights On Or Off At Night?

New aquarium owners often have a lot of questions, and one of the most common concerns is how to properly light their aquariums. Lighting your Aquarium properly can show off your fish’s vibrant colors, help you diagnose any issues in the tank, and even control your fish’s feeding and resting schedules. However, having aquarium lights has its downsides too. Prolonged exposure can harm not only your fish but also the Aquarium’s ecosystem. It can also stimulate rapid growth in some plants and slow growth in others and even cause death in some cases. In this article, we will talk about the effects of leaving the lights on at night.

Do Aquarium Fish Need Lights on Or Off at Night?

Aquarium lighting can be complicated because it’s so difficult to achieve the ideal balance, especially when trying to keep fish in an aquarium filled with living things from different environments. While it’s true that most freshwater fish need some level of lighting in order to eat and do fish stuff, however, keeping them in constant bright light without darkness will cause stress. Leaving your lights on all night would also cause other issues.

All aquarium fish get stressed out when the lights are left on for a long time at night because it disrupts their resting cycle, leading to various health problems that can be fatal sometimes. Algae growth can also be stimulated by an excess of light in the tank, which is something you want to avoid. The heat generated by some aquarium lights can also cause problems with the water’s balance, especially in a smaller aquarium, so you may really need to turn off your aquarium lights occasionally.

Your fish should be kept in conditions that are as close as possible to those they would experience in the wild. Many fish and plants could be hurt by too much of anything, so be careful about that. In order to keep your fish healthy and fit in the tank, you should provide them with as much light as possible without exceeding their maximum requirement. 

Problems With Leaving the Lights On at Night

Adding an aquarium light will not only make your tank look better, but it will also help you in many other ways. However, your Aquarium shouldn’t be exposed to bright sunlight for extended periods of time. Read on to learn 5 telltale signs that your aquarium plants are being overexposed to light.

1. Fish Stressor

You shouldn’t leave the aquarium light on all night because the fish won’t be able to tell the difference between day and night, and their rest patterns will be disrupted. Eventually, it will have a negative effect on their health while accelerating the growth of algae.

2. Overgrowth Of Algae

The most important reason to turn off the aquarium light at night is to prevent algae from growing too much. If the light stays on 24 hours a day, algae will surely take over the tank. Unlike plants, which only do photosynthesis at fixed durations, algae will keep doing it around the clock.

3. Negative Effects on Fish Health

Stress brought on by excessive light can be detrimental to your fish. A fish that’s stressed can easily catch a number of diseases, some of which could be fatal. Your fish will be agitated and have trouble resting if the lights in their tank are left on all night.

4. Reduce Plant Growth For Certain Plants

Most plants can live and make food with no more than 12 hours of light, but if you leave the lights on in your Aquarium at night, photosynthesis won’t stop. It will keep going until there is no more carbon dioxide which slows the growth rate of plants in the tank. If these gasses aren’t in the right amounts, they will not only hurt your plants, but also your fish.

5. Rapid Plant Growth For Certain Plants

One of the first things you might notice if you leave the aquarium light at night is that aquarium plants grow quickly. The plants will grow quickly if there are enough nutrients, CO2, and light. This will make your water plants grow much faster and take over your tank, so you may have to trim them more than usual.

6. Excessive Light and Heat

There are some aquarium lights that produce both light and heat. The temperature should stay pretty much the same all day long, especially in smaller aquariums; these lights can also make the water temperature rise a lot, which could kill your fish and plants. It’s not a good idea to use lights that affect the water temperature in an aquarium because the sudden change in temperature can shock the inhabitants.

7. Death of Certain Plants

It may come as a shock, but aquarium plants can actually die from too much light. Even though plants rely on light for growth, excess light can actually hamper the growth of some plants. When plants produce more energy than they can use, reactive oxygen is released, which can be lethal to the plant.

How Long Should Your Aquarium’s Lights Be On For?

When considering aquarium lighting options, one common question is how often the lights should be turned on. Aquarium lighting is important, and it does a lot more than just light up the beauty of your Aquarium. Light is essential for the growth of everything that is alive in your Aquarium, but too much of it can be harmful, so you should always check how much light your tank gets.

The recommended amount of light for animals and plants is between 10 and 12 hours per day. For hassle-free lighting, set a timer or buy a product that has a timer built in so you don’t have to check your lighting every once in a while. You can also set your aquarium light on when you’re inside your home and turn it off once you leave for work.

Plants and fish benefit greatly from light, but it can stress the fish and cause abnormality to the growth of plants when there’s too much of it. Keep in mind that algae, like other organisms, grow quickly in bright conditions. If you see that algae are starting to grow, you should reduce the time the light is on.

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Do Fish Need Blue Light at Night?

Lighting, as any aquarist will tell you, is crucial to the health of an aquarium’s inhabitants. All of the fish in the tank will benefit from the Aquarium’s lighting, so it is important that you should pick the appropriate color of light for your tank. In fact, not only does it aid in the fish’s development and metabolism, but it also speeds up their rate of growth.

People often call these blue lights “moonlight,” and their main purpose is to help you see your nocturnal fish at night. Some fish, like certain species of catfish, prefer the darkness of night or the absence of artificial light, so providing them with a moonlight aquarium will make them feel at ease. Blue light doesn’t necessarily affect the fish in your Aquarium, so they might not need it, but it could be a good option if you want to keep the lights on at night. Blue light is also a great choice of light because it doesn’t heat up the water as much as other colors do, and it also helps plants grow and makes the colors of your fish really stand out.

Even though blue lights may look nice, they are still not natural for an underwater environment. It also doesn’t do much for the fish, so it doesn’t have to be a certain color. In the end, blue light is great for your tank as long as you don’t use too much of it, so whether or not you use it is up to you.


Do Goldfish Need Light at Night?

All fish should be kept on a regular day/night schedule, even goldfish. Since goldfish don’t have eyelids, they need total darkness to rest. Leaving the aquarium lights on at night can keep them from getting enough sleep.

Do Mollies Need Light at Night?

Molly fish don’t come out at night, so they don’t need a light on. In fact, molly fish need  darkness during night time so they can rest.

Do Betta Fish Need Light at Night?

Betta fish like to sleep in the dark but need light to wake up. If you have an aquarium light, you should turn it on when you wake up and turn it off when you go to bed.

Do Fish Need Light During the Day?

Fish in aquariums need light to know if it’s day or night. However,  your fish don’t need to have an extra light in their Aquarium as the natural light in the room is already enough.

Do Fish Need Total Darkness at Night?

Fish don’t have to sleep in total darkness, but it’s best to give them as much darkness as they would get in their natural habitat. They might fall asleep even if the lights are still on, but their sleep and health will be better if they can sleep in the dark.


Animals can’t talk to us like people do, so it can be hard to figure out what they need. This is particularly true with a fish, whose actions are much harder for humans to understand than that of a cat or dog. Your fish can’t really complain if they are getting too little or too much light, especially at night. But through the experience of aquarists as a whole, we have learned that keeping the lights on for longer than fish are used to can have bad effects on them. Keeping your fish healthy really comes down to making an environment that is similar to what the fish would experience in its natural habitat.

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