Should Fish Tank Light Be On All The Time? (Solved!)

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Okay, so you get your fish tank and set it up with lights. Then you leave the lights on 24/7. But wait! Should fish tank lights be on all the time?

No, fish tank light should not be on all the time because it gives rise to algae growth and also stresses the fish. Aquarium fish require an alternating period of darkness and light just like in their natural habitat and so it is recommended to keep the lights on for only 8-12 hours a day.

Keeping the lights on 24/7 is one of the biggest mistakes that many beginner fish keepers make. But don’t worry because thankfully, you are in the right place.

In this article, I’m going to tell you when should you keep your lights on, should you keep lights off at night or not, plus answers to many more related questions you might be having right now.

So to clear all your doubts continue reading till the end!

And if you prefer watching videos then you can also watch my following video!

How long should you keep the light on in a fish tank?

In general, aquarium lights should be kept on for 8-12 hours a day. Like every other organism, fish also have a biological clock and they understand the day-night cycle. So the fishkeeper must maintain the day-night lighting schedule in the fish tank.

Planted tanks are a little different from other tanks because in them you have to take care of your plants as well as your fish.

Aquarium plants definitely need light to grow. But that doesn’t mean that you need to give them light all the time.

There’s a limit to their absorption capacity. So after a certain period of time even if you keep the lights on in your planted fish tank it would be of no use to your aquarium plants.

Instead, you would start seeing the growth of hair algae and brown algae.

For tropical freshwater tanks and fish-only tanks, there’s not much to say. Just follow the general rule of keeping the light on for 8-12 hours a day and be consistent with it.

Always remember, the more you can mimic the natural lighting, the better it is!

For saltwater tanks, follow the same range of 8-12 hours of lighting. However, if you have corals and you know the exact lighting period of their natural habitat then it would be best to mimic that natural lighting period.

Should I turn my fish tank light off at night?

Yes, you should turn the fish tank light off at night because it prevents algae growth, and also the fish assumes it as their resting period. Remember, aquarium fish also requires an alternating period of light and darkness just as they would in their natural environment.

You will notice after you turn off the lights, after some time all the fish in your aquarium will go near the bottom of the tank and start resting.

This resting period is what we can call their sleeping period. During this time the fish reduces most of their metabolic activities.

Another benefit that you could get if you leave the light off during the night, is reduced algae growth in your tank.

As I discussed in my article can you keep a fish tank near a window, algae just love a good amount of light.

Like plants, algae can also produce food using photosynthesis.

So the more amount of light your aquarium gets throughout the day, the more algae growth you will see.

(algal bloom in fish tank turning it into green)

This can also lead to algae bloom in which the whole tank would turn completely green.

What is the best time to turn on the aquarium light?

The best time to turn on the aquarium light is during the sunrise time or a few hours later. Like every other organism on earth, aquarium fish also follow the day-night cycle and so it is best to follow the same fish tank lighting schedule.

Personally speaking, at our home we just turn on all the aquarium lights about 8:00 a.m. and turn them off in the evening 6:00 p.m.

Thus, in this way we give almost around 10 hours of light to our fish in a day. And following this schedule, there’s no major issue so far.

So you can also do the same.

But, if you are seeing algal blooms by keeping lights on for 12 hours a day then you can just keep on the lights for about 8 hours.

Then you can just start with small hours and gradually increase the lighting period.

Remember, you have to mimic nature so 10-12 hours will be sufficient. So you don’t need to give the aquarium more than 12 hours of lighting period.

See what works best for you and do accordingly.

Also, note that you need to be “consistent” with the fish tank lighting schedule. If you are a responsible person to turn on and off the aquarium lights manually, then it is well and good.

But what if you can’t? Don’t worry, because there are cheap and good quality timers available on amazon like the BN-LINK 24 Hour Plug-in Mechanical Timer which will automate this process for you.

So you can check that out if interested.

Can too much light kill fish?

Although too much light may not kill the fish, giving more than 12 hours of light to the fish is not good. The fish will get stressed and even change in color.

A study was done on marine angelfish and it was found that lighting does influence the fish color.

See, if on some days, you forget to turn off the lights and you have enough hiding areas in your tank then it is ok. But keeping the lights on 24/7 is definitely not recommended.

If lights are kept on all the time, fish will find it difficult to take rest. Without proper rest, they will get stressed and you may see them fighting with one another.

Also, because of stress, you may notice changes in their eating habits.

Moreover, if you use aquarium lights such as incandescent, VHO-fluorescent, and metal halides, then they can cause heating issues inside the tank.

For big fish tanks it is ok but for small ones this, not a great idea. And according to, sometimes in small aquariums, this light can cause an increase in temperature such that, fish and plants can even get killed.

So instead it is good to use the LED lights in the fish tank.

The LED lights not only produce less heat but also consume less electricity and have many color options.

Long story short, you should not keep the aquarium lights on all the time.

See Related: Moonlight For Aquariums – Top 5 Things You Should Consider!

Can fish live without light?

Although aquarium fish may survive without light if there is an ambiance light near the fish tank. But improper lighting can cause a color change, stress the fish, and can even make them lethargic.

I have a friend who keeps his goldfish in a tank without any light. They feed the fish, do water changing and that’s it. Their fish are in okayish condition.

The tank receives ambiance light but the fish don’t look very active. Also, the water always seems to be cloudy because of algae.

According to, fish such as goldfish will lose color and some even stop eating if they are kept without lighting.

So my takeaway from all this is if you want your fish to be healthy and fit then never keep your fish without light.

Lights not only allow the fish to feel the day-night cycle but it is also pleasant for us as a hobbyist to watch the fish playing around in the fish tank. Isn’t it?

You May Also Like To Read: How Long To Wait To Put Fish In Tank After Conditioner?

Related Questions

Fish tank light on or off on vacation?

Fish require both darkness and light similar to their natural habitat so it is best to keep a timer that turns the light on and off automatically. However, if you are going on a vacation then the best option is to leave your aquarium under the care of your friend, neighbour, or someone you trust.

Is it better to leave aquarium light on or off?

The aquarium light should be left on for not more than 8 -12 hours a day. Leaving the light on for more than 12 hours would stress the fish as they would find it difficult to rest and it will also cause algae growth in the aquarium.

Do fish need light in aquarium?

Yes, aquarium fish do need light during the day but not more than 8-12 hours a day. Like other organisms, fish also follow the circadian rhythms and so they require the alternating period of darkness and light in a day.

Can fish sleep with light on?

Yes, fish can sleep with the light on because they have internal biological clocks that tell them when to take a rest. However, it not good to let the fish sleep with lights on because they will find it difficult, and secondly algae growth will also increase in the tank.

Is it OK to leave fish in the dark?

Yes, it is perfectly fine to leave fish in the dark but only for the night. It is recommended to mimic the natural environment of the fish and so aquarium fish must be kept for an alternating period of darkness and light in a day.

Are fish scared of the dark?

No, fish are not scared of the dark. Although a sudden change in light might scare the fish because they don’t have well-developed iris. The main function of the iris is to control the amount of light entering the eyes. But it is momentary and soon the fish settle down.

Final Thoughts

That’s it! I hope you found this article helpful. Below I am sharing the link to my other fishkeeping articles which you might like to read. So check that out if interested. Till then thanks and have a happy fishkeeping day.

Read More:

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