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Can I Leave my Aquarium Light on 24/7?

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Being an aquarist, I often found myself struggling with the question of aquarium lightning. To be more specific, I wasn’t sure whether I should leave the lights 24/7 or instead turn them off during the night. Luckily, over the years, I researched that topic quite profoundly. Now, I am willing to share my experience.

It isn’t recommended to leave the aquarium light on 24/7 since it won’t allow the fish to distinguish between day and night and disrupt their sleep. Eventually, it will negatively impact their health and force accelerated algae growth. Instead, it is better to leave the lights on for 10-12 hours.

As we proceed, I will show you what 24/7 lightning could do to your fish and teach you a trick you may implement if you keep forgetting your aquarium lights on during the night. Eventually, I’ll share what kind of light fish can tolerate, even when they are sleeping.

Can I Leave my Aquarium Light on 24/7?

Yes, technically, you can. However, is it a good idea? Well, no, it isn’t. Not if you want a healthy aquarium with happy fish and an appropriate collection of plants and algae. Lighting is crucial to aquariums. However, quantity is just as important as quality. 

When it comes to leaving the aquarium light 24/7, please consider the following:

The Affect on Fish

As you now know, aquarium lighting controls a fish’s habits. It tells them when to sleep and rest and when to wake up and resume their activities. 

What does this tell you? Well, fish require a certain amount of light every single day. But they also require a certain amount of darkness. By keeping the lights on all day and all night, you are depriving them of that darkness.

This will throw their circadian rhythm off balance, destroying their daily routine in the long run. Even more problematic is the fact that it will prevent them from falling asleep at night. While aquarium fish can live without light, they cannot survive without sleep.

Constant lighting will keep them awake. This will induce stress, not only weakening their immune system but making them vulnerable to all sorts of diseases. They will become listless and lethargic during the daytime.

Their appetite will also suffer. Some fish may respond to this situation by manifesting signs of aggression. Others will settle into an inactive state. Humans can sleep in the presence of light if they are tired enough. But many aquarium fish are not that clever.

The Affect on Plants

Fish are not your only concern when it comes to leaving the aquarium lights on during the night. You should also consider the plants. First of all, aquariums need plants. Some fish can live without them. But most species appreciate the privacy they offer. 

Therefore, you cannot afford to solve the consequences of 24/7 lighting on plants by merely removing the plants. That will induce stress in your aquarium since your fish will no longer have places to hide and reproduce.

Plants require light to grow. It is necessary for photosynthesis to occur. They consume carbon dioxide and produce oxygen. If you have an oxygen-deficiency in your water, a properly lit planted tank can solve it.

On the other hand, 24/7 darkness will reduce oxygen levels because the plants will take oxygen and produce carbon dioxide. This isn’t an issue if your plants are artificial. However, if you grow real vegetation in your tank, that factor worth considering.

24/7 lighting won’t harm your plants directly. Nevertheless, it will elevate the growth of algae.[1] You don’t want the algae in your tank to run amok. It will consume the resources your plants require to survive. If your plants die, the stress their absence induces in fish may kill them.

Can 24/7 Lighting Affect the Conditions in the Tank?

24/7 lighting won’t stop at merely preventing your fish from sleeping. If you have incandescent lighting, it will raise the temperature of your water.[2] Your aquarium must remain within a specific range where the temperature is concerned to permit your fish to thrive.

Without periods of darkness, incandescent lighting can cause the water temperature to skyrocket, killing your fish in the process. That is especially true for relatively large lightning sources that hang just above the waterline.

Can You Keep the Light on at Night Without Harming Your Fish?

As was mentioned above, fish require darkness at night to rest. But what if you want to look at them? Is there a way to illuminate the tank without disturbing the fish? The answer is blue light.

Blue LED light mimics the moon, whose light is present in the wild, which means that fish can tolerate it at night.[3] Blue lighting is prevalent in many circles because it allows you to see your tank’s contents, and yet, fish cannot see it.

Blue lighting allows nocturnal species to see, although it is unlikely to wake sleeping fish. Red light has a similar impact. It will illuminate your tank. Yet your fish can’t see it, so their sleep will go undisturbed.

In other words, you can use ordinary lighting during the day. Then, you can switch to gentle blue or red LED light at night. For that purpose, I use the NICREW ClassicLED Plus Planted Aquarium Light (link to Amazon). That device got two lightning modes; one for the day and one for the night.

How Long Should You Leave Aquarium Lights On?

It is usually best to leave the aquarium lights on for 10-12 hours. However, some cases require fewer hours of lightning. That applies to aquariums that are relatively new, occupy mainly bottom dwellers, have plenty of algae, or those that are situated in areas with sufficient ambient lighting.

As you can see, the lightning periods depend on multiple factors:

When it comes to new tanks, you will do just fine with an average of 10 hours of lightning. As your tank matures, you can add one hour of light to the schedule every so often until you reach the 12-hour-mark. Observe the tank during this period. If you notice any adverse side effects, cut back on the hours.

The volume of algae you observe will also determine the hours of light your tank requires. Simply put, if the algae population is growing too quickly, your tank is getting too much light. You should cut back.[4] If the amount of light isn’t the problem, the intensity might be the issue. 

Either way, your only option is to keep adjusting the lighting hours until the algae growth level stabilizes. The type of fish should also inform your decision. For instance, bottom dwellers do not require that much light because they occupy the water’s murkier sections in the wild that receive very little light.

Tropical fish, on the other hand, are accustomed to 12 hours of light on most days.[5] Fish in colder regions where daylight lasts just a few hours can survive on four or five hours of light a day, possibly even less. You also have fish like minnows and danios from areas where the daylight hours change every season.[6]

In such cases, you have to alter the amount of aquarium light they get throughout the year. If you ask your retailer, they will educate you on the lighting requirements of the fish you just bought. Though, in many cases, you can identify the lighting requirements on your own by locating the region where the fish in question originates. 

All you have to do is replicate the lighting conditions it would typically encounter in the wild. Some fish do not require light at all. A prominent example is the blind cave Mexican Tetra. It lives in a location in the wild that doesn’t receive any natural light.[7]

Lastly, aquariums situated in rooms with plenty of ambient lighting require fewer hours of artificial lighting.[8] Some people use ambient lighting to illuminate their aquariums in the daytime. This is an acceptable practice if the room in question is properly lit. Though, you are discouraged from placing the aquarium in direct sunlight. The algae population will explode.

Do Fish Need Light?

Do aquarium fish require lighting? Well, surprisingly, they don’t.[9] To be more specific, most aquarium fish do not have any biological processes or components that require light. Yet, they did not evolve to live in the darkness. In other words, you are still expected to give them light.

What Purpose Does Aquarium Light Serve?

While fish do not require light, you are encouraged to keep your aquarium lit because it serves several purposes, including:

  • Routine – This is the essential aspect of aquarium lighting. It generates a routine for your fish and creates a clear line between night and day for the creatures. This same routine exists in the wild. 

Fish can differentiate between night and day in lakes, rivers, and ponds because, in many places, the sun tends to rise and set at roughly the same time every single day. By programming your aquarium lights to do the same, you will create a healthy schedule for your fish, making certain that they always eat and sleep on time.

  • Illumination – Light allows aquarists to see their fish. People buy fish because they want to observe their beautiful colors. Without light, you cannot see your fish not unless the ambient light is bright enough to illuminate the contents of your aquarium.
  • Colors – The presence of aquarium lighting will enhance the colors of your fish. It darkens the color pigments, giving the fish a richer, more vibrant appearance.[10] Some people use clever lighting to transform fish with a dull appearance, allowing their colors to pop.
  • Sleep – Aquarium lighting will determine your fish’s sleeping habits. If you did not know, fish sleep. Still, they don’t all sleep the same way. Some fish become completely immobile, while others will continue to hover. You also have those that remain in motion during the night, though their movements are sluggish. 

Either way, fish sleep. More importantly, they need sleep. And most importantly, most of them require darkness to fall asleep. You can use the lighting in your aquarium to create a healthy sleeping/waking cycle for your fish. Their health will improve in the long run.

Should I Leave my Tank Lights on While on Vacation?

You shouldn’t leave your tank lights on when you go on vacation. However, you shouldn’t leave them off either. Generally, it is best to install lights with a timer. This will ensure that the lights switch on and off at the exact same time every day regardless of your presence or absence.

To achieve that, I usually recommend getting the BN-LINK 24 Hour Plug-in Mechanical Timer (link to Amazon). All you have to do is set the lightning hours and plug in your lightning cable. The device will take care of the rest.

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It would be best not to leave the aquarium lights on 24/7. During the night, fish require darkness to sleep correctly. You may also compromise your fish’s inner clock by leaving the lights on during the night. That may end up with lethargic and sick fish.

However, you may use blue LEDs during the night. This type of light resembles the moonlight fish enjoy in the wild. If you keep forgetting the lights on or go on vacation, you may use a plug-in mechanical timer.