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What is the light in a fish tank for? (Do you really need it?)

If you are wondering what is the light in a fish tank for and if you even need one then you are in the right place.

In this article, I am going to answer the same question.

I will also answer the other questions you may have related to aquarium light.

So let’s get into it.

So, what is the light in a fish tank for?

The light in the fish tank is to enhance the appearance of the fish so you can enjoy your fish tank. Besides, if you have live aquarium plants in your tank then the light is necessary for them for the process of photosynthesis to create their own food.

What is the light in a fish tank for? (Do you really need it?) image

Why aquarium light is necessary for a fish tank?

There are several reasons you need an aquarium light in your fish tank.

1. Enjoy your fish tank

Aquarium light illuminates the fish tank so you can clearly see the fish in your aquarium.

Besides, aquarium light enhances the appearance of the fish and they look vivid under aquarium light.

And that’s the whole point of an aquarium. You want to enjoy the activities of the fish in your tank. And aquarium light enhances that experience.

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2. Emulate the day and night cycle

In your fish tank, you’re responsible for the health of the fish in your aquarium.

And the best way to keep your aquarium fish healthy and active is to try to emulate there natural habitat as much as you can.

And aquarium light helps you to do the same!

In their natural habitat, fish has a natural day and night cycle.

It is not necessary that the fish will experience the same day and night cycle in the fish tank, especially, if the tank is located in a room where there’s no ambient light.

So, to emulate the natural day-night cycle, you should equip your tank with an aquarium light. And keep the light on anywhere between 8 to 12 hours every day.

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3. Live aquarium plants

If you have live aquarium plants in your fish tank then the light is very important for the proper and healthy growth of live aquarium plants.

Live aquarium plants need light to prepare their own food by the process of photosynthesis.

You can check out my recommended light here

Too much light is also harmful!

fish tank with algae

Feature image – Author: Berger Licensed by CC BY 2.0 Resized and Cropped

Ok, now that you know that aquarium light is essential for maintaining a healthy aquarium. But, just as with everything else, too much light is also bad for the inhabitants in your aquarium.

Too much light can cause several issues in your fish tank:

  • If you provide too much light then it can cause rapid algae growth in your tank.
  • Too much light is also bad for fish because it breaks their day and night cycle. This causes stress and if it continues to happen then it can also lead to the death of the fish.

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How many hours a day should aquarium light be on?

fish tank with aquarium light on

Feature image – Author: Pete Brown Licensed by CC BY 2.0 Cropped and resized

You can keep light on for anywhere between 8 to 12 hours every day in your fish tank.

Now, this is a very wide range. 

This is because how much light you should provide to your aquarium really depends on the setup of your aquarium.

There are several factors that come into play when it comes to deciding how much time you should keep the aquarium lights on in your fish tank.

1. Live aquarium plants

Light is not as important to the fish in your aquarium as it is for the live aquarium plants.

The live aquarium plants make their own food by the process of photosynthesis for which they require light.

If you have live aquarium plants in your tank then you will need to provide them light according to their needs.

For low light aquarium plants, keeping aquarium light for 8 hours every day is enough.

On the other hand, for light-demanding aquarium plants, you’ll need to keep the lights on for up to 12 hours every day.

Overall, if you have live aquarium plants in your tank then you should find out their lighting needs. And then provide light according to their needs.

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2. Fish species

Most of the fish can do well in any lighting environment.

The light in the aquarium is more for you than the fish in your aquarium. Aquarium light is necessary so you can see the fish and enjoy your aquarium.

Most of the fish don’t mind getting too much light in the aquarium.

In fact, most of the fish actually get more light in the aquarium than they get in their natural habitat.

However, there are some fish species like Cichlids and Tetras, which in their natural habitat, live most of the time in the darker environment.

So providing too much light to such fish can affect them negatively.

So when it comes to light for the aquarium fish, you should try to mimic their natural habitat.

A general rule is-

  • For a tropical fish aquarium, you should provide light up to 12 hours every day. This could be a combination of aquarium light and ambient light.
  • For cold-water fish, you should provide the light anywhere between 8 to 10 hours every day.

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3. Ambient light

How much ambient light is already present in the room where your aquarium is located is also an important factor to consider when you’re providing additional light in your aquarium.

If you have a fish only tank and it is placed in a well-lit area then you may not need to provide additional light in your aquarium.

However, if you have some live plants in your tank then, even though, the aquarium is located in a well-lit area still you’ll need to provide additional light through aquarium light.

Because the ambient light is indirect which is not ideal for photosynthesis.

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4. Heat due to aquarium light

There are a few types of aquarium light that not only provide light but they can also heat up the water in your aquarium.

The types of aquarium light that can heat up the water in your aquarium include 

  • metallic halide
  • Incandescent
  • VHO fluorescent

Now, heating of the water due to the aquarium light is usually not an issue in larger tank of 55 gallons or more.

Because these aquariums contain a lot of water and the heat gets distributed throughout the tank.

However, in the smaller tanks, the water can get pretty hot due to the heat produced by aquarium light.

It can get so hot that it can kill the inhabitants like the fish and plants in your tank.

Ideally, you should get an LED aquarium light fixture for your aquarium.

The LED aquarium lights don’t heat up the water in the tank.

Besides, there are several benefits of LED aquarium light-

  • LED aquarium lights are cost-effective i.e. they don’t consume a lot of electricity
  • LED aquarium lights come in different color spectrums
  • They also last longer than other types of aquarium lights.

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5. Algae

Probably the most reliable way to figure out how much light you should provide in your aquarium is by monitoring the algae growth in your tank.

The different types of algae growth in your aquarium can tell you different stories.

Brown algae

Brown algae occur when there are a lot of nutrients in your aquarium but your aquarium doesn’t have enough light.

Plants require optimum light to consume the nutrients.

So, in this case, the plants in your aquarium are not getting enough light to consume all the nutrients. This can cause brown algae in the aquarium.

Overall, brown algae is a very good sign that suggests that you’re not providing sufficient light in your aquarium.

So, in this case, you should increase the hours of light you provide in your aquarium.

Or you should increase the intensity of light in your aquarium.

One important thing to keep in mind if you have a newly setup tank is, in newly set up tanks, brown algae is very normal. 

This brown algae is also known as Diatoms.

So if you have a new setup and you are noticing brown algae in your tank then you don’t need to do anything.

After a few weeks, the brown algae will get replaced by the green algae automatically.

Besides, there are a few ways to reduce the brown algae if you want to do so:

  • You can siphon it off using a siphon
  • You can also introduce some algae eaters like snails and shrimp to get rid of brown algae in new setups.

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Green algae

Green algae growth occurs when you are providing too much light in your aquarium along with a lot of nutrients.

If you have live aquarium plants and if you are providing optimum light in your aquarium then the aquarium plants will grow as fast as they can because they are getting the light along with the nutrients.

But when you are providing too much light then the green algae will take advantage of the light and the remaining nutrients and grow in your aquarium.

So if you notice green algae in your tank then you should reduce the time of light you provide in your aquarium.

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6. It is a trial and error process

Exactly how many hours of light you should provide in your aquarium is really dependent on the setup of your aquarium i.e. the live plants and the fish you have in your tank, and the ambient light already present in the room where your aquarium is located, etc.

So there is no one answer that fits all the setups!

You should start by providing 8 hours of light in your aquarium and keep it going for at least 2 to 3 weeks.

If you don’t notice any algae growth in your tank then you can increase the light for one more hour every day.

If you still don’t notice algae growth in your aquarium then you can again increase one more hour of light in your aquarium every day.

However, if you notice algae in your tank after increasing the light then you should reduce the light again. And this is how you can find out exactly how many hours you should keep the lights in your aquarium on every day.

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Consistency is important

fish tank with aquarium light on

Feature image – Author: Eric Gillingham Licensed by CC BY 2.0 Cropped and resized

Once you know how many hours of light you should provide in your aquarium then being consistent with the light is also very important.

If you are not consistent with the light then this can cause algae growth in your aquarium.

Many aquarists struggle with maintaining consistency with the aquarium light.

Fortunately, there’s a cheap and reliable way to maintain consistency with the aquarium light.

You can get a timer for your aquarium light!

The timer will turn on and off the light at the same time every day.

It is very convenient!

I recommend Nearpow timer. You can check it out at Amazon here

As you can see it is very cheap. You can even set the timing for a whole week in this timer.

This feature especially comes in handy when you are on vacation.

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What is the blue light in a fish tank for?

There are a few benefits of blue light in a fish tank.

The blue light is usually kept on during the night time. However, keeping the blue light on all night is not recommended.

Nocturnal fish

If you have a nocturnal fish in your aquarium then as these fish stay active during the night, if you keep the blue lights on during the night then it can help them to see in the tank clearly and forage for food in the aquarium.

Aesthetics

Many people keep the blue light on during the night because it looks cool.

Besides, when you keep the blue lights on, you clearly see the fish and all the inhabitants in your tank.

Plant growth

The blue spectrum is the most important spectrum that helps in the process of photosynthesis to the plants.

Avoid the sudden shock

When you turn on your aquarium light in the morning or turn off your aquarium light at night the fish can get a little bit shock.

But before starting your aquarium light, if you turn on the blue light for about an hour before starting the main aquarium light and turn on the blue light after turning off of the main aquarium light for about an hour, it can help to avoid the sudden shock.

However, this is not a very big deal for fish.

Even when you don’t turn on and off the blue light or didn’t use blue light at all in your aquarium, the fish will get used to the routine of the aquarium light turning on and off.

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Should you keep the blue lights on during the night?

As you can see above I have mentioned several benefits of blue light.

Usually, people keep the blue lights on during the night for a couple of hours.

It is not recommended to keep the blue lights on all night.

This is because if you keep the lights on during the night then this can cause algae growth in your tank.

You should only keep the blue light on after you have turned off the main aquarium light for about an hour.

You can also turn on the blue aquarium light before turning on the main aquarium light in the morning.

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Conclusion

Overall, aquarium light is one of the most essential parts of your aquarium.

This helps you to see your aquarium clearly and if you have live aquarium plants in your tank then it helps them in the process of photosynthesis.

I hope you found this article helpful.

If you do, please share it.

Happy fishkeeping!

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