How Long Should You Leave Aquarium Lights On—The Light Schedule (2023)

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There is no doubt light is crucial for both plants and fish in aquariums,whether warm or cold water.

But, how long should you leave the lights on?

Frankly, there is no simple answer to this question since there are manyvariables to consider, and only a person telling you as much is beingtruthful.

That said, assuming everything remains constant, you will need 10hours of light daily for an average aquarium.

However, tropical fish and plants, do better with 12 light hours a day,while cold water fish and plants will thrive with just 8 light hoursdaily.

Of course, if you only have fish and no plants in the aquarium, lesslight is required.

To better understand your aquarium light needs, let’s dig a littledeeper, even look at a few fixtures that offer adequate full spectrumlighting inline with your tank needs.

Aquarium Light Schedule

To start with, you want an aquarium light schedule to help you keep tabs of your lighttimings.

Conventionally, your plan should include the hours and time of day youwant your lights to run, and a timer like this Nicrew unit to help you monitor your plan rest you forget.

Then simply set the timer to turn the lights off at the same timeeach evening and to turn them back on the next morning.

For instance, I’ve scheduled my planted tanklight to runalmost all day.

It includes this Nicrew LED Gen 2 light that remains 10 hours daily, which is enough for my fish to feed and plants to thrive, though I onlygrow low-light plantspecies, though the light will work even for high-light plants.

This LED fixture should give off a dark blue light that mimickmoonlight, which will adequately illuminate the aquarium even at nightwithout disrupting the fish or plants night cycle. And is equally usefulwhen you have visitors over at night.

That said, there are a few things to consider before setting up yourlight schedule. So, below are insightful answers you’ll find usefulprior to starting:

Does Your Fish Tank Need Light

Well, if you are going to enjoy the aesthetics of your fish in theaquarium, you will definitely need light. Not only that, your fish needthe light to feed and engage in other fishy activities, but also a fewhours of darkness to relax and unwind.

Moreover, some fish species like goldfish may fade in the absence ofadequate light.


Having said that, one important thing to keep in mind is differentfreshwater fish will have varying light needs.

Top and mid-tank dwelling fish will benefit from light better than bottom dwellers, such as plecos, catfish, and loaches, which are accustomed to living at the base of water bodies where light is scarce.

Fishys native to the tropics will perhaps also enjoy more light than those from subtropical regions where the sun does not penetrate the surface of the water as much.

Tropical Freshwater Fish Light Needs

Most common tropical fish come from rivers, streams and clear lakes inwarm regions and are used to bright sunlight and warming rays in thenatural 12-hours cycle.

Therefore, to best recreate these conditions in your aquarium, provide12 hours of light a day, preferably, with bright LEDs that penetrate thewater surface or make use of sunlight when you have a well-lit aquariumroom..

However, some species of tropical freshwater fish liketetras mayprefer low light. In which case, you leave enough hiding spaces in yourtank for these fish to get away.

Cold Water Fish Light

Normally, cold water fish don’t have to be overly illuminated, onlywhen you need to enjoy your aquarium, so anywhere in the region of8hours of light is adequate.

However, if you’ve got enough hiding spaces for them, even 12 lighthours are Ok, especially when your tanks hold light-hungry plants too.

To create the optimal environment for cold water species, try to matchyour aquarium lighting to seasonal daylight hours akin to those in thetemperate region where most cold water species come from.

Top and Medium Dwelling Aqaurium Fish Light Needs

As we saw above, top and mid-level dwelling fish are used to (and prefer) more and brighter light exposure than bottom-dwelling fish.

A light period anywhere from 10 to 12 hours a day should be enough, but ensure the light is not obstructed and adequately penetrates the water surface.

Therefore, when keeping most of these fish, you do not want too many floating plants forming a canopy at the surface of your tank.

Bottom Dwelling Aqaurium Fish Light Needs

Bottom-dwelling fish, unlike their top and mid-level cousins, do not need as many light hours. Anywhere from 8 hours daily should be sufficient.

A canopy of floating plants at the water surface is also recommended, especially if you have bright light or a wide-shallow tank.

You will also note that most bottom-dwelling species prefer to feed at night but spend most of the day hiding. So, add a lot of hiding spaces in your tank, and preferably, allow more light for your bottom-dwellers at night.

Do Aquarium Fish Need Light During The Day

Yes, most tropical aquarium fish need light during the day since they are used to the daily light cycle with 12 hours of light followed by a period of darkness.

(Video) Should Aquarium Lights Always Be On? How Long? (All Doubts Solved!)

However, shy bottom-dwelling fish will prefer dimmer light, both at night and during the day. They are nocturnal.

Breeding females, sick or stressed fish also seem to like a lesser light during the day, perhaps to get the much-needed rest.

One way to ensure all your fish enjoy their preferred light levels during the day is adding hiding places in the tank using plants, driftwood, and other decorations.

Do Aquarium Fish Need Sunlight

Tropical aquarium fish do not need sunlight per se. However, placing your fish tank in an area with daylight exposure will help save on your lighting bill during the day.

Moreover, if you have plants in your aquarium, they will benefit from sunlight, which is more natural than any aquarium light fixture.

If you decide to allow sunlight in your fish tank during the day, keep in mind the duration should not be too long (more than 10 hours) because it will promote algae growth.

Too much light exposure will also increase the temperature in your fish tank, which might help save on power bills, but can be challenging to control because you can’t turn it off as you would do an aquarium heater…

…and moving a fish tank full of water, plants, decorations, and fish away from the sun is not an easy fit.

Light Needs for Live Aquatic Plants

While light in fish tanks is partly for your viewing pleasure, plantsdepend on diurnal light patterns a lot, and good quality light isparamount. (See how to choose planted aquariumlights).

However, the light used in your aquarium and the duration the light stayon will depend on the plants you have.

Some plants will thrive in low lights while others need high light forlonger. Low light plants like Javamoss, Javafern, andAnubias specieswill be fine with 8 to 10 hours of low-intensity light a day andthe plants are perfect forbeginners.

On the other hand, light hungry species prefer longer light hours,somewhere in the region of 12 hours a day, CO2 addition and fertilizerdosing.

That said, I also recommend you match your aquatic plants to the type offish you have in your tank; tropical plants with tropical fish.

Ideally, keep platies, guppies,betta and corycatfish in aquariumsplanted with Java fern, Java moss anubias,hornwort, andCryptocoryne.

Goldfish, minnows,ricefish, and Zebradanios come fromtemperate zones where daylight hours fluctuate, and are best paired withAnubias species and tiger lotus.

Light and Algae Growth

The most prominent con of keeping your lights on for long is algae.Usually, if you let the lights in your aquarium to run for more than 12hours a day, blue-greenalgaewill establish exponentially.

(Video) Lighting your Aquarium - When and how long?

Although it’s not just your aquarium light you should be concernedabout. but also natural light from the sun. Thus, when you have your tankin a brightly-illuminated room, placing it too close to the window isnot recommended.

That said, algae will probably grow in your aquarium anyway, whether toomuch light or not, so what is important is to keep the extent in check.

In case of algae thriving in your tank even in fairly low light,consider adding algae eaters siamese algae eaters,shrimplike ghost and Amano, Amanoshrimp, andsnails (mystery,nerite).

Should You Leave Aquariums Lights on at Nights

Proper aquarium lighting is essential to fish and plants, but so is theperiod of darkness for them to rest and replenish. Thus, it’s best toturn off your aquarium lights at night to mimic plants and fish naturallight cycle.

In case you weren’t aware, fish do sleep, however, most species don’thave eyelids, and depend on you to switch off the lights and provideenough hours of pure darkness for them to catch a nap.

Keep your aquarium light on for the recommended 8 to 12 hours then turnoff the light to mimic the natural day and night cycle.

In case your fish gets restless when the lights go out, turn off theroom overhead light an hour before your tank lights. This should givethe fish eyes an hour to adjust to the lower light setting beforecomplete darkness.

Do Aquarium Fish Need Light at Night

As I stated in the paragraph above, most tropical aquarium fish only need a maximum of 12 hours of light a day, followed by a period of darkness. Preferably, this should follow the daily light cycle.

As such, most of your fishes may probably not need light at night unless they are nocturnal bottom-dwelling fish or inverts like snails that prefer to feed at night.

For purposes of your aquarium aesthetics, you can use moonlight aquarium bulbs to illuminate your tank at night. The calm lighting will accentuate your aquarium but still allow your finny friends to get some sleep.

Please see this post (Do aquarium Fish Need Light at Night) for more insight.

How to Light Your Aquarium While Away on Vacation

Most people will remember to feed their fish when leaving for vacationbut fewer remember to schedule their aquarium lights for when they areaway.

While some aquarists are not even sure whether to leave the lights on oroff while they have a good time away from home.

Frankly, fish in your aquarium doesn’t need light to live, henceleaving the lights off is fine. If anything, leaving the lights oncould be a fire hazard and will encourage algae growth.

But if you have plants in your aquarium, then you will need to leavethe lights on with a timer (recommended) running a diurnal setting.

Alternatively, if your aquarium room is properly illuminated, leave thetank near a window to take advantage of the natural day-night cycle.

(Video) How long should Aquarium lights be on?

Heat Emitting Lights and Aquarium Temperature

This is most likely not the first thing to cross your mind, but apartfrom light, aquarium fixtures produce heat, meaning you’ll have toconsider that when choosing the light fixtures and bulbs.

This is especially true for smaller aquariums where the possibleincrease in temperature can be significant.

Generally, metal halides and incadescent bulb produce a lot of heat and aretherefore not the best for aquariums. Besides, incadescent technologyis pretty much outdated.

The more obvious and appropriate light source would, therefore, beeither LED or fluorescent, but given the two, LEDs are the harderhitter.

Consider full spectrum LED rated for both aquarium plants and fish,preferably with night mode.

A thing to note if you choose to go with fluorescent; T5 or T8fluorescent lights are not synonymous with VHO-fluorescent, which likemetal halides, will spike your aquarium water temperature.

Also, T5 bulbs are preferable (as opposed to T8 and T12) because oftheir skinny bulbs, narrow footprint, availability, efficiency, and lowheat output.

My Two Cents

Each aquarium environment is different, thus the only sure way to knowhow long to keep aquarium light on is trying out different setting untilyou find the perfect fit.

Even so, consider variables like natural and ambient lighting sinceevery home is inherently unique.

First, think of your plants before the fish since fish tanks are lessfussy about lighting. If anything, lighting a fish tanks is mostly foryour own amusement.

Then do a little due diligence before buying or replacing aquarium growlights, compare different products in the market to make sure you getthe best bargain.

Moreover, since the question is how long your lights should remain on,and we’ve established the solution is a good light schedule, seriouslyconsider a programmable light fixture with a timer, or maybe LED nightmode lights.

If you are located in the USA (more so Florida) and are looking to buy tropical (freshwater ) mentioned in this or any other post (and more), check out Consolidated Fish Farms Inc.

Also Consider usingAquariawise Coupon Code for a 10 percent discount on eligible purchase. They are a great source for healthy aquarium fish, plus we get a small commission with no extra cost to you.

Enjoy Your Aquarium.


How long should aquarium lights be on? ›

How long should I keep my aquarium lights on? To provide animals and plants the lighting they need, 10 to 12 hours a day is sufficient. Installing a timer or purchasing a unit with integrated timing can make lighting easier––just set it and forget it. Keep in mind algae loves light as well.

How long should I leave my lights on in a planted aquarium? ›

Most planted aquariums do not need more than 8 hours of light. Setting your lighting period for longer than 6 hours in NEW planted aquarium set-ups. During the first month your lighting period should be shorter to keep away algae while your plants grow in.

How long should you leave lights off after adding fish? ›

Keep aquarium lights off for at least four hours after the new arrival is introduced into the aquarium. Most invertebrates and marine plants are more sensitive than fish to salinity changes.

Do LED lights disturb fish? ›

How Lighting Affects Fish. Fish are not as reliant on light as plants. In general, aquarium owners can use incandescent, fluorescent, or LED lights for fish but should be aware of the heat issues that incandescent lights cause.

Can Too Much light hurt fish? ›

However, if you use all 12 hours of aquarium lighting when the tank's already in a bright and sunny room, you're at risk of providing the plants and fish with too much light. Too much light isn't only bad for plants, but it's bad for fish. That's because it causes stress and prevents them from being able to sleep.

What do fish do when the lights are off? ›

Fish don't like the dark because when there is no light to see, they dart around the tank, colliding with the walls, ornaments and can even become tangled in the plants. Fish need light to determine whether it is night or day, and they're scared of the sudden switch from darkness to light.

Can aquarium plants get too much light? ›

So, yes. You can give your aquarium too much light, which can be bad. Too much light can make the fish stressed and can additionally cause rapid algae growth, higher water temperatures, and the deaths of certain species of aquatic plants.


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