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How long you leave the lights on in your aquarium could significantly affect your fish and plants' health. Determining the optimal time to leave the aquarium lights on could be pretty confusing. However, understanding the importance of lighting is the key to keeping the inhabitants of your planted tank happy.

The answer to how long you should leave the aquarium in a planted tank is not a simple one. There are several factors to consider, and this guide will reveal all of them.

We're going to cover several aspects of lighting in your aquarium, including the types of plants, types of light, ambient light, and kinds of fish. We also answer some nagging questions you might have about aquarium lighting.

Factors that Determine the Lighting of Your Aquarium 

If you just got a new aquarium, it would be better to keep the lights off for most of the day - at least until the inhabitants get more accustomed to it. This way, you get to control algae growth, and your plants will get comfortable around the fishes in the aquarium.

The lighting needs of aquariums differ by various factors, some of which we will discuss below.

Types of Aquarium Plants 

This is the most crucial factor. Even though all plants need light for photosynthesis, the intensity and type of light may differ.

During the photosynthesis process, some plants could require up to 12 hours of light daily to produce the food necessary to stay healthy.

However, distinct requirements will depend on the amount of light a plant will need in a day. The size and species of the plant are essential factors to consider. There are generally three types of plants you should learn about if you're considering your tank's lighting requirements.

Here they are!

1. Carpet Plants

You can find these plants at the very bottom of the aquarium. As the name suggests, they often cover the aquarium base similarly to a carpet. Carpet plants are the most demanding in terms of sunlight. They require about medium to high light.

This means you have to keep the light on for at least 12-14 hours so that your plants stay healthy and in good condition. The most popular carpet plants and their light requirements are:

Lilaeopsis: This popular carpet plant will thrive if you supply it with medium to high light. If the fishes in your plant will not do well with 12-14 hours of light daily and only need a moderate amount of light, this will be an excellent choice for you. The carpet plant can grow comfortably in medium light without bringing any harm to your fish. 

Dwarf Baby Tears: You don't need a large tank to keep this wonderful-looking carpet plant. The Dwarf Baby Tears will thrive and flourish in even shallow aquariums so long as you provide them with enough light to stay healthy. You should set out a specific period to leave the lights on in your aquarium, usually between 12-14 hours, so your plants are healthy. 

2. Mid-Level Plants

Mid-level/ground plants don't require as much maintenance or sunlight as carpet plants.

Mid-ground plants need only about moderate to a low amount of light. This should translate to about 8 hours daily, which is adequate for plants to grow and thrive in the aquarium.

All you have to do to keep the plants looking good in your aquarium is to monitor them and ensure that they get their required lighting needs. The most popular mid-level plants you can find in a lot of aquariums are:

Pygmy Chain Sword: These plants have a striking appearance that resembles grass, and if you're down with that idea, they would be a great addition to your aquarium. The Pygmy Chain sword plant is stunning and low maintenance, making them one of the most popular plants for aquariums. You do have to keep in mind that they might have adverse effects on intense lights, and because of that, we recommend gentle lights.

Green Tiger Lotus: This plant will survive on its own with almost no care from its owners. Its light requirements are medium, and it will shine brightly and wonderfully in your tank so long as it keeps growing fine without external challenges.

3. Background Plants

Besides beautifying your plants or adding to your tank's aesthetics, background plants can help you hide equipment in the tank, add a little more depth to your aquarium, and give your fishes a comfortable place to hide.

You don't need to spend a lot of time caring for background plants if you provide them with the light they need to grow and flourish. The most popular background plants are:

Pondweed: This plant will develop exceptionally in environments with high light. It will also be all right in environments with medium light levels; however, it might not develop as well as it would have in bright light. The growth of plants depends on the light you expose to it, so if you don't give the plants as much light as it needs to grow correctly, it might grow stunted.

Amazon Sword: You need to give Amazon swords low to medium light daily to grow comfortably. You don't have to buy an expensive lighting system to keep this plant satisfied in your tank.

Ambient Room Lighting

The ambient light in your room or the area you keep your aquarium is another essential factor you need to consider. If you keep your aquarium in an outdoor location, you might not need to put artificial light in it.

If your aquarium is in a brightly lit area, you will not need as much artificial light as dimly lit areas. 8-12 hours of light will be too much for aquariums in rooms with a lot of ambient light. A couple of hours a day is more than enough.

Artificial light is always better than ambient room light as artificial light is direct and ambient light is indirect.

Algae Growth

The light in your aquarium boosts algae growth. Hence, it would be best to regulate aquarium lighting according to the algae growth in your tank. Too many algae can cause severe problems in your tank and destabilize the already established ecosystem.

Another detail you should keep in mind is that sunlight fosters more algae growth than artificial light. So, if a lot of your aquarium light is ambient, you might have more algae in your tank than others.

Types of Light You Have? 

There are many light options when choosing artificial light for your aquarium, each with its advantages and disadvantages. The two main options are:

Fluorescent Bulbs: There are two common fluorescent bulbs for aquariums, namely T8 and T5. Both bulbs will provide sufficient light for aquarium plants, but if you want to go for the best, it would be the T5 bulbs. They are far more powerful than others, and they will work well for tanks with dense populations. You only need 1 or 2 bulbs for a medium tank, depending on your plant's needs.

LED Light: These are more cost-effective than fluorescent bulbs but are also as powerful. Although you have to install more LED lights than fluorescent bulbs, they could last for at least five years. These lights will also add a terrific aesthetic to your aquarium and produce significant lighting effects.

Lighting Needs for Your Fish 

Just like other living creatures, fishes also need light to engage in their natural activities. You should only take away the light when they need to rest or relax.

While some fishes will be just fine with little or no sunlight, others such as goldfish may begin to fade if you don't give them enough light. Different fishes have unique needs. Here’s what you need to know about the lighting needs for tropical freshwater fishes and cold-water fishes.

Tropical Freshwater Fish

You can find tropical fishes in streams, clear lakes, and rivers in warm areas, so they've grown accustomed to bright light for a day cycle of 12 hours. If you have tropical fishes in your tank, you'll have to recreate their natural habitat.

Give your tropical fishes about 12 hours of light daily, usually with bright lights like LED. These lights can easily penetrate the surface of the water just like sunlight would. 

Not all tropical freshwater fishes will like bright light as some species like tetras will not be comfortable. A good alternative is to have plenty of hiding spaces in your tank so the fishes can stay there when the light becomes too much for them.

Cold Water Fish

Coldwater fishes don't need a lot of sunlight - only 8 hours of light will be sufficient. But if you have many hiding places in your tank, you can keep the lights on for up to 12 hours.

The optimum light conditions for your cold-water fish will be similar to what it is in temperate regions since that is their natural habitat. Always try to match your seasonal daylight hours with that of temperate regions.


Should you leave aquarium lights on at night?

No. Even though plants and fish need light to survive, darkness is also necessary. If you keep the lights off at night, the plants will burn off all the accumulated starch from the day so they can grow properly. Fish also need the darkness so they can relax or sleep after all their activities during the day.

If you give them more light exposure than they need, it could also kill the fish and plants. Extended exposure to light may interfere with the plant’s photosynthesis and make them wither when the toxins become too much.

How to regularize your lighting when you’re on vacation?

Many people remember that their fish will need to eat when they're on vacation but fail to remember they will also need light. Some assume it doesn't matter whether you leave the lights on/off, but that couldn't be more wrong. 

While leaving the lights off might not affect the fish as much, it could be dangerous for the plants. It would be better to use a timer to regulate the tank's lights or put it near a window to stay illuminated.

Can I leave my aquarium light on 24/7?

It would be dangerous to leave your aquarium lights on 24/7 for both your plants and fishes. Firstly, it will make your aquarium a breeding ground for algae because they grow faster with light. If you do not remove the algae in your tank, it could create an imbalance in your tank or even make your fishes sick.

Constant light will also affect the sleeping patterns of your fish, and it can make them stressed. If you continue with this, their immune system will weaken over time, and the fishes will eventually die. 


Determining the lighting needs of your tank is not an easy task. You need to carry out intensive research into the types of plants and fishes you have in your tank. Remember to consider the kind of light too, because it is also a significant factor.

If you're also planning a vacation while preparing for what your fishes will eat, you should also plan for the light in your tank, especially if you have many planted plants. The key to it all is to create an environment similar to their natural habitat, and you should be good.

About the author 


My name is Eric. I'm the owner of snugaquarium.net and a writer with a passion for aquariums and fish-keeping. I love to watch the three different species of freshwater fish floating around in my homemade aquarium in my spare time.

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