Should You Leave the Aquarium Light on Overnight?

New aquarium owners often have a lot of questions about aquarium maintenance.

One such common query is whether you should leave the aquarium light on overnight or not.

The short answer is No – you SHOULD NOT leave the aquarium light on overnight.

Fish require both light and darkness to survive. Like most other animals, fish need darkness to rest. The fact that they lack eyelids makes them require a sufficiently dark environment for them to get in any kind of sleep or rest.

If you are in the habit of leaving the aquarium light on 24/7 or forget to turn it off sometimes, stop that immediately. Your fish need the darkness to stay healthy and happy. Give them that.

Why is Light Necessary for Aquarium fishes?

Fish need light about 8 to 12 hours of light, depending on the types of fish in your aquarium. They need light to go about their business each day, and a lack of it can cause them to become lethargic.

This can result in them eating less food and possibly become sick. Some fish like goldfish can even lose their color if they’re not exposed to enough light every day.

Who wants a goldfish that isn’t gold, right?

Light is necessary not just for the fish in your aquarium but also for any natural plants you may have in it. Plants need light for photosynthesis to survive and grow.

A lack of light will cause them to wither away with time, and you’ll need to replace them to keep your aquarium looking fresh and green.

Fish Need to Sleep Too

A number of different fish species do not have eyelids which may give the impression that they don’t sleep. That is not the case, however.

Considering that many don’t have eyelids, it is essential that their nights are dark enough for them to rest up.

Lack of rest or sleep can cause your fish to be restless and lethargic the next day. This lethargy can be stress-inducing and can cause the fish to eat less or not at all. Your fish could get sick that way and even end up dying due to the lack of energy.

Fish need the energy to eat, swim, and live. Rest is extremely important for the survival of your fishes and you need to make sure you give them the darkness they need by turning off the aquarium light.

If possible, keep the aquarium in a place that is dark after sunset (even if your house lights are on). If that is difficult to do, consider getting a cover that prevents light from getting through and place it over and around the aquarium.

You may have noticed that when you turn the light on the next morning, your fish are relatively still at the bottom of the aquarium. This is how some fish sleep, and it can be thought of as something similar to the way humans daydream.

Fish don’t have REM sleep as many animals do, but they need rest all the same. Leaving your aquarium light on all night will prevent them from doing that.

Like human beings, fish also get stressed, and constant light is a big contributor to that stress. This can even possibly lead to your fish acting-out their stress, resulting in fights with other inhabitants in your aquarium. Keep those to a minimum for your fishes’ sake and for yours.

A happy pet will make you a happy pet owner.

Do your best to keep your fish comfortable at all times. A good balance of light and darkness will help emulate a regular day and reduce their stress in the process.

Regulate Your Fishes’ Time of Day to What Is Best for Them

Ideally, you should try and replicate the natural cycle of day and night according to the season. All animals have a body clock that tells them when they should wake or sleep. It coincides with the natural day-night cycle.

Therefore, it is best to turn on your aquarium light on when it’s daytime and turn it off when it’s a night to avoid any problems for your fishes.

Your fishes require anywhere between 8 to 12 hours of light depending on the kind of species they are. Look up the ideal requirements of light duration for your fishes and set a routine that gives them the best environment. You could also change the duration according to the changes in seasons, which shouldn’t be much change anyway.

If your daily work schedule is different from a regular 9 to 5 workday, or if you’re generally awake all night, alter the light schedule accordingly. Most people want the light to be turned on when they’re awake so they can see their pets.

For those of you who are nocturnal and keep your fish tank’s light on in the night, be sure to turn it off in the day.

In addition to that, ensure that the room the aquarium is in is dark even during the day. This time should replicate the night time and it is essential that the fish get a dark atmosphere for half the day.

If your schedule forces you to stay up at night, you could also consider getting nocturnal fish for your aquarium. That way you don’t have to worry about bringing in any confusion with their body clock and the day-night schedule you want to set for them.

You can watch your pets swimming happily in the night and rest easy knowing you’re not disrupting how they would naturally function.

Whatever your schedule is, you should be consistent with when you turn on and off the aquarium’s light. If you are sticking to replicating the natural day-night cycle, don’t alter it if you have guests coming over in the night.

Abrupt changes in the light schedule will cause your fish to be disoriented and make them restless in the process. Keep your pets comfortable and happy. That is your duty as a pet owner.

If you really want to have some kind of light to keep on in the night to show your guests or friends your fish in the night, you could get a moonlight that emits a dim light that can help you see your fish and will help them sleep at the same time.

Compare your fishes’ activity with and without a moonlight before you decide to keep one indefinitely, however, observe each morning if they look to be sleeping the same way with and without the moonlight.

Get rid of the moon-light if you notice that your fishes seem more active in the mornings of using the moonlight. It is more important that your fishes are well-rested than it is for you or your guests to watch them go about their lives through the glass.

Algae Formation Increases with Excessive Light

Leaving the light on can also cause an excessive build-up of algae in your aquarium. Algae need light to grow and there will be no break in the growth process if the light is turned on at all times. This growth is expedited even more so when there are natural plants in your aquarium.

Excessive algae growth will make cleaning the aquarium a nightmare. It will begin to cover your plants, decorations, and the glass of the aquarium. This will require more frequent cleaning of the entire aquarium and will be much more work when you do so.

You’re better off curtailing the algae growth and preventing a dirty-looking aquarium before its due cleaning-time. This will also help save you from additional tiresome work that can be avoided with ease.

Algae are an important part of aquatic life. They are a good source of food for some fish species and shouldn’t be removed from your aquarium completely. Your aim, instead, should be to keep it in control so that your aquarium looks clean, and so that you don’t have to clean it too frequently.

Light and Heat

There are some light bulbs that emit light and cause heat simultaneously. This happens more with metal halides and incandescent bulbs and can alter the temperature to a greater extent in smaller aquariums than in larger ones.

These lights should be avoided for aquarium use because it will cause a discrepancy in the temperature when you turn it on and off. The temperature should be more or less consistent throughout the day. In smaller aquariums, these bulbs can also cause a great rise in the water temperature, possibly killing your fish and plants in the process.

The best temperature is the one closest to the one in the fish’s natural environment. Some freshwater fish require higher temperatures than others. Make sure you know which is best for the species you’ve kept as your pets and keep the temperature according to that.

There are also light bulbs sold in the market that are advertised as both heating and illuminating. For the same reasons mentioned above, using such bulbs for your aquarium is not the best idea. It is even worse if you’ve got a relatively small aquarium.

Your best bet for an aquarium light is an LED bulb. The light emitted from these bulbs penetrates the water sufficiently, giving your pets enough light during the day. You can then add a separate heater to maintain the temperature in your aquarium.

When choosing natural plants to accompany your fish in the aquarium, be sure to pick those which are from a similar habitat as your fish.

If the plant needs a colder climate than what your fish require, there is a chance that the plant will dehydrate due to excessive heat and die. A dead plant that you don’t notice soon after it has died can become a problem for your fish.

Try Out Automatic Dimmer

If you’re worried that you have to stay at work late and no one is home to turn the aquarium light off, you don’t need to worry. There are things that can do that without your help.

You can get an automatic dimmer that turns on and off at specific times of the day. You can then stay consistent with the light-darkness balance without having you to do anything other than set timers.

Or else you can buy LED lights that can be controlled using your phone app. That will allow you to dim the light even if you’re not at home.

Keeping a pet, regardless of what kind, is a huge responsibility – one that shouldn’t be taken lightly no matter the situation.

One important step in respecting that responsibility is by being punctual with the time you turn on and off the light for your aquarium. You will harm your fish by varying the time of day for them.

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