How Long To Leave Aquarium Lights On In A Planted Tank? All Your Answers Here!

Last Updated on February 9, 2022 by Marco C.

Do you know how long to leave aquarium lights on in a planted tank? Learn about this very important information by reading our article.

We have done all the research to teach you exactly how long to leave your aquarium lights on in a planted tank.  For the most part, every aquarium tank uses lights.

Lights are one the most important aspects of growing aquarium plants successfully.  They are the “sun” for the plants in your tank.  In nature, water plants take the sun from the atmosphere to perform photosynthesis.

Photosynthesis is nature’s process of using sunlight to produce oxygen.  Without light, plants are unable to survive.  If you are not keeping your fish tank outdoors, then you will need to use light.

The only other case in that you may not need to use lights is if you have an unplanted tank.  This means a tank with no plants, just fish.  

But, plants play such a great role in a fish tank ecosystem because it provides oxygen, clean the water, and can balance everything.  So why not have a planted tank?  If you are ready to get started with a fish tank with plants you came to the right place.

We will answer the crucial question: how long to leave aquarium lights on in a planted tank?

Keep reading now!

Basic Facts About Aquarium Lights For Plants

According to Duke University in the United States, lights play two purposes in your tank.   “It highlights and shows off your fish’s colors and provides critical energy for plants (if present).”

So it has an aesthetic purpose of making your fish look good and of course, it helps your plants grow.  When you first get started with your aquarium, you may notice that there are many light options for your tank.  

Don’t get overwhelmed by these choices.  You have to choose your lights based on the types of plants and aquarium you want.  

Some plants require lots of light to survive.  While others do not need much and are considered a low light plant.  If you are a beginner, it is best to start with low-light plants.  

This is because the lights not only help the plants in your system grow but also stimulate the growth of algae.  If you have too much light, it is likely that you will have high algal blooms. 

high algal blooms

Learn more about: The Best Aquarium Light To Prevent Algae

Algae can be a nuisance if not handled properly.  If there are too much algae, your tank may experience nitrification which will ultimately kill your fish if not fixed.  Also, when there are frequent algal blooms, you will have to clean your tank more often.

This can be a lot of work.  If you don’t have a well-balanced system set up, then we suggest starting with low light plants to practice.

Some good low-light fish tank plants are Anubias Barteri,  African Water fern, and java moss.  But there are plenty more options.  Find which one suits your tank the best.

You can also put special fish in your tank to eat the algae.  But ultimately, it’s better to avoid this problem altogether by sticking to low-light plants. 

How Long Should Aquarium Lights Be On?

Typically, the lights you see in an aquarium are fluorescent bulbs.  People tend to use T5 or T8 fluorescent lights for aquarium purposes.  A T5 bulb is more powerful than T8.

So if you want to only use one light and have an aquarium with a lot of plants packed together, a T5 would be a good choice.  

Your next question is probably: How long to leave aquarium lights on in a planted tank?  Once you set up your lights, it is recommended to leave them on between 6-8 hours. 

Typically in nature, most plants require that amount of sunlight per day to thrive.  So we are just mimicking nature with our lights.  

There are dangers of leaving your aquarium lights on for too long or too short.   If you leave your lights on for longer than 8 hours a day, you promote high algae growth.  

When you leave the lights on for too short, your plants will not grow properly.  Once your tank is established and looking healthy, you should set a timer to ensure that the plants receive the exact same amount of sunlight per day. 

The optimum time frame to set your timer is for 8 hours a day.  

However, when you first plant out a tank, it is recommended to only provide 6 hours a day.  This is to give your new plants a chance to establish themselves without too much competition from algae.  By setting your lights for less time, less algae will grow. 

Take your time on this step.  Once you notice that your plants are growing new leaves and look healthy, you can start to increase your lighting periods.

Best Planted Tank Lighting Schedule

In terms of when to keep your lights on – it’s very simple.  Just follow the natural rhythms of the sun in your local area.   Set the timer so it starts in the morning until evening.  

After that, you can sit back, relax, and let nature do the work. 

You can control the power and strength of your lights as well by choosing the right bulbs.  Always assess the amount of light needed for the size of your tank.  Of course, larger tanks require higher lighting power. 

There are other types of bulbs you can consider as well.  Some people prefer to use LED lights in their tanks.  The type of bulb you use will not affect how long to leave aquarium lights on in a planted tank.  

As you may see from reading this article, understanding lights is not a very difficult task.  But, it is essential to have a beautiful and healthy fish tank! 

Hopefully, now you understand exactly how long to leave aquarium lights on in a planted tank.  Give it a try and let us know about your experience in the comments below. 

Feel free to ask questions! We are always happy to help!

Read more about: Planted Aquarium Lighting Calculator


How long should aquarium lights be on?

Once you set up your lights, it is recommended to leave them on between 6-8 hours.