Is It Bad to Leave The Fish Tank Light On 24/7?

Estimated read time 7 min read

The importance of lighting in your fish tank can’t be overlooked.

Light helps your plants grow and allows you to recreate the day/night cycle, which in turn keeps your fish rested and healthy.

Plus, light allows you to see what’s going on inside that little world that you hold dominion over!

But you might be wondering, is it bad to leave your fish tank on all the time? The answer is yes, the lighting in your tank should only be on for a maximum of 12 hours and even less if you don’t have live plants.

Too much light can lead to health problems for your fish as well as issues with algae.

That said, too little light and your plants might not get the energy they need to create the food they need to grow.

It’s all a tough balance to achieve, and each tank is different.

With that out of the way, let’s get into a bit more detail about the lights in your aquarium.

Great Lighting Options


Do Fish Need Light?

Fish do not need light to survive. In fact, there are many species of fish that live at very low depths where there is no light at all, and they live just fine.

That said, keeping an aquarium lighting schedule with periods of darkness and light is just good practice for most tropical fish as this recreates the natural day/night cycle that occurs on earth.

Plants, on the other hand, do require light to convert Co2 into energy through photosynthesis.

Depending on what you have in your aquarium will determine just how much light you require.

How Does Light Affect Fish?

The type and duration of your aquarium’s lighting can affect fish, especially when we use artificial lighting.

In fact, as noted by The Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB):

Artificial light blurs the boundary between day and night and therefore interferes with fish’s physiological functions and behavior. It is already known that artificial light affects fish’s growth and development and can even disrupt the spawning migration of diadromous (migratory) fish.

How Long Should You Leave Your Aquarium Light On?

Most fish will do great with about 8 -10 hours of light. However, live plants tend to require about 10-12 hours of light each day.

So it really depends on what you are keeping in your tank and how you set it up.

The best way to set it and forget it is to purchase a timer for your lights or buying a light that comes with a built in timer – trust me, this makes your life so much easier.

Below we’ve provided a very general aquarium lighting schedule that you can use when you first set up your tank.

But monitor your plants and the behavior of your fish and adjust it accordingly.

How Much Light Does Your Aquarium Need?

Stocking LevelHours Of Light
Tropical Fish Only8-10 Hours Daily
Tropical Fish & Plants10 Hours Daily
Heavily Planted12 Hours Daily
Coldwater Fish & Plants8 Hours Daily
Coldwater Fish Only8 Hours Or Less Daily

When Should I Turn My Fish Tank Light Off At Night?

This is up to you; it really doesn’t matter when your lights come on or off as long as you have the duration dialed in.

For example;

I have three aquariums in my house, one in the living room, and the other two are in my kid’s rooms.

The living room aquarium light turns on at 11 am and stays on until about 9 pm, only 10 hours total.

The other two aquariums come on at about 12 pm and turn off at about 8 pm – this is because my children need to fall asleep. But the fish still get about 8 hours of daylight.

Keep in mind that although my aquariums don’t turn their lights on until midday, the aquarium is still likely getting some natural ambient light all day through the windows in the house.

Do Fish Need Darkness To Sleep?

Fish do need a period of darkness to rest and sleep, so it’s best to keep your lights on a schedule that allows for a day/night schedule.

This will ensure that your fish get the rest they need, keep stress levels low, and limit the amount of algae growth that can sometimes be caused by too much light.

Blue Aquarium Night Lighting (Moonlight)

Depending on the type of lights you might be using for your aquarium, you might see an option for Blue Aquarium Light; this is sometimes referred to as Moonlighting or Night Lighting.

Typically this option is found on most modern LED light fixtures.

That said, this option is cause for a lot of confusion in the hobby, and you might be wondering what exactly this blue light is for and what it does.

Let’s answer those questions below.

What Does Blue Aquarium Light Do In A Fish Tank?

In a freshwater aquarium, the blue light gives the appearance of moonlight shimmering down into the aquarium. Don’t worry, though; the blue light won’t affect any of the fish or plant life in your tank.

That said, the blue light you see in a saltwater setup has many benefits and is an essential piece if you are setting up a saltwater aquarium.

Can Fish See Blue Light?

No, the fish still think it’s dark, but the blue light is great for owners of nocturnal fish so they can see what the fish are doing in the dark.

Can Fish Sleep With Blue Light On?

Yes, fish have no problem sleeping when the blue light is on. As mentioned above, blue light is used to give the appearance of moonlight shimmering down into the aquarium.

Are LED Lights Good For Fish?

As we mentioned above, the use of artificial lights can affect your fish’s behavior, breeding, and sleeping habits.

That said, I use LED lights on all my fish tanks, and my fish are all super healthy, and I’ve never experienced any issues.

If you are not into LED lights, then be aware that there are many other options like incandescent, fluorescent & metal halide lights.

However, these alternatives tend to use more power than LED lights and give off much more heat.

LED lights to use less power, give off almost no heat at all, and have a variety of colors and uses available as well as fully customizable settings, which comes in handy for planted tanks.

Does Your Fish Tank Need Light?

Yes, most fish tanks will require some form of light.

Whether it’s for the live plants in your tank, or to recreate the natural day/night cycle or so you can see your nocturnal buddies at night with a blue light.

Adding a light to your tank is a good idea in most cases.

Take care of your fish.

Further Reading: Learn Why Aquarium Lights Are One Piece Of A Few Essential Aquarium Equipment We Recommend.

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