How Long Should You Leave Aquarium Lights On
By Eddie Waithaka @aquariawise
Updated, 11, Aug, 2022.
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 many variables to consider, and only a person telling you as much is being truthful.
That said, assuming everything remains constant…
A fish tank (aquarium) needs 10 hours of light daily. However, tropical fish and plants, do best with 12 light hours a day, while cold water fish and plants will thrive with just 8 light hours daily.
Of course, if you only have fish and no plants in the aquarium, less light is required.
To better understand your aquarium light needs, let’s dig a little deeper, even look at a few fixtures that offer adequate full spectrum lighting inline with your tank needs.
Do Fish Tanks Need Light
Yes, fish tanks need lights to help you see your fish better, assist your fish find their way around the tank, and your aquatic plants to grow. Aquarium lights bring out the colors in your fish (moreso at night) and help your plant synthesis nutrients leaving them healthy, lush and green.
Fish tank lights also help some tropical fish, such as ram cichlids and guppies while breeding and nocturnal, bottom dwelling species to feed at night.
Does Your Fish Tank Need Light
Well, to enjoy the aesthetics of fish in an aquarium, you will definitely need light in your fish tank. Not only that, your fish need the light to feed and engage in other fishy activities, but also a few hours of darkness to relax and unwind.
Besides, some fish species like goldfish may fade in the absence of adequate light and your ram cichlids may not breed without light.
Do Fish Need Light
Fish need light in a tank (aquarium) but these may vary between species. Different freshwater 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.
Tropical fish will also enjoy more light (+light hours) than those from temperate subtropical regions where the sun does not penetrate the surface of the water as much.
Now, if by fish needing light you meant in the wild, well, that depends on the native water bodies and the level they swim in. Fish from tropical regions in Africa, Central American, Australia, the northern countries of South America, and most of Asia are accustomed to 12 hours of light a day, year round, so they pretty much need light to go about their business.
It’s what they are used to…
…unless they are catfish, plecos or loaches that swim in the murky, dark bottom parts of rivers and lakes.
Do Tropical Fish Need Light
Tropical fish need light in their tank perhaps more than subtropical fish. However, it will depend on the water level your fish prefers. Top dwelling tropical fish, such as betta and most mid-level fish, like guppies, tetras, cichlids and more, do better in a well lit tanks since sunlight penetrates the water in their wild habitat as well.
That said, tropical bottom fish, like plecos, catfish and loaches that are more accustomed to the bottom part of rivers, lakes, and swamps, where the sunlight rarely penetrates do not require as much light in their tank since they are used to living and feeding in relative darkness.
In fact, when you have tropical plecos, loaches, and catfish with other fish in your fish tank, its recommended you dim or turn off the lights for a period everyday to help keep them comfortable.
Do Fish Need Light At Night
Many fish do not need light at night because they feed, swim, and enjoy other finny things in the 8 to 12 hours coicinding with day time, then sleep the rest of the time. However, skittish fish, like kuhli loaches and bristlenose plecos, may require light at night, because they are too shy to come out and feed under bright light (such as daylight).
Aquatic snails, shrimp, crabs, and other bottom dwelling fish are also hide within the plants during the day and come out to feed under low-light at night.
Now, if you have a mix of top fish with bottom fish and need to leave your aqurium light on at night, I suggest using moonlight aquarium bulbs, which are bright enough for you skittish feed to eat at night and calming for top fish that need to rest, and with minimal effect on algae growth.
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.
Most of your aquarium 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.
Do 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. 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.
Should You Leave Aquarium Lights on During The Day
You should not always leave your aquarium light on during the day unless your fish tank is in a dark spot with limited access to sunlight. As long as your fish gets 8 to 12 hours of light each day, the source does not matter.
Leaving your aquarium light on while there is sunlight is wasteful. Besides, algae will develop and thrive in a tank lit under daylight, since alga thive unders excess light.
However, keep in mind light is essential for your fish tank and I recommend making it available during the day. So, you should turn on the light on your fish tank during the day if the light coming into your house is not enough for your fish and plants.
Should I Turn Fish Tank Lights Off at Night
Proper aquarium lighting is essential to fish and plants, but so is the period of darkness for them to rest and replenish.
It’s best to turn off your aquarium lights at night to mimic plants and fish natural light cycle. You should turn off the light at night (just after dusk) to allow your fish sometime to sleep, unless you have skittish, nocturnal species that feed at night or in low light.
Keep your aquarium light on for the recommended 8 to 12 hours then turn off the light to mimic the natural day and night cycle.
In case your fish gets restless when the lights go out, turn off the room overhead light an hour before your tank lights. This should give the fish eyes an hour to adjust to the lower light setting before complete darkness.
Granted you may not be aware, fish do sleep.
However, most species don’t have eyelids, and depend on you to switch off the lights and provide enough hours of pure darkness for them to catch a nap.
Best Time to Turn On Aquarium Lights
The best time to turn on aquarium lights is in the morning between six and eight, depending on the season and daylight hours, and leave them on for between 8 and 12 hours; turn them off anytime from 5 to 8 p.m However, if your fish tank is in a well lit spot, where it can access sunlight (not direct) all day, you may not need to turn on the lights during the day.
Aquarium lights during the day are best left to people with tanks in basements, dark corners and what have you (unless they are for aesthetics), since much light and longer light hours will aid algae growth in your aquarium, something no tank owner wants.
After the 8 to 12 hours day period with your aquarium lights on, turn them off for the next 12 or so hours to allow your fish some down time, but its ok to leave dim light or blue-light-bulbs if you have nortcunal fish and critters in your fish tank.
How long Should You Leave Aquarium Lights On
Your aquarium lights should be left on for 8 hours if you have sub-tropical and bottom dwelling fish and up to 12 hours for tropical fish tanks. The lights are best left on during the day (between 7 a.m to 7 p.m) to mimic the average tropical daylight hours.
However (as noted before), this will depend on how much sunlight your fish tank is getting during the day. You do not want your aquarium to have to much light because of algae.
Better still, regulate the intesity of your light bulbs depending on the amount of natural light getting to your fish tank.
How Long Should Can You Leave Your Aquarium Lights Off
You can leave your aquarium lights off for up to 24 hours a day if the fish tank is getting enough natural light during the day. However, on gloomy days, you can only leave the lights off for a maximum of 12 to 14 hours depending on the fish and plants in you have.
8 to 12 hours of darkness or low light will give your fish ample time to sleep and renergize before starting the next day, the same amount of time they rest at night in the wild.
When Should Aquarium Light Be on
Your aquarium light should be on when you there is no enough natural or ambient light getting to your fish tank, such as on overcast days or when you have a fish tank in a dark place, like a basement or garage, starting around 6 a.m (sunrise) to 6 p.m (sunset).
You fish tank light can also be on at night when you need to bring out the aesthetics of your fish tank, such as when frineds come over. Even so, consider programmable moonligt bulbs for night use since they bring out your finnies colors better and are come enough for tropical fish that need to rest during night hours.
However, this should only be during the day (between 6 a.m and 8 p.m). At night its is ok if your leave the lights off.
You also need to keep in mind how much light the fish and plants in your fish tank require to help you regulate the intesity at any given time.
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.
Aquarium Light Schedule
To start with, you want an aquarium light schedule to help you keep tabs of your light timings.
Conventionally, your plan should include the hours and time of day you want 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 time each evening and to turn them back on the next morning.
For instance, I’ve scheduled my planted tank light to run almost 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 only grow low-light plant species, though the light will work even for high-light plants.
This LED fixture should give off a dark blue light that mimick moonlight, which will adequately illuminate the aquarium even at night without disrupting the fish or plants night cycle. And is equally useful when you have visitors over at night.
That said, there are a few things to consider before setting up your light schedule. So, below are insightful answers you’ll find useful prior to starting:
Tropical Freshwater Fish Light Needs
Most common tropical fish come from rivers, streams and clear lakes in warm regions and are used to bright sunlight and warming rays in the natural 12-hours cycle.
Therefore, to best recreate these conditions in your aquarium, provide 12 hours of light a day, preferably, with bright LEDs that penetrate the water surface or make use of sunlight when you have a well-lit aquarium room..
However, some species of tropical freshwater fish like tetras may prefer low light. In which case, you leave enough hiding spaces in your tank for these fish to get away.
Cold Water Fish Light
Normally, cold water fish don’t have to be overly illuminated, only when you need to enjoy your aquarium, so anywhere in the region of 8hours of light is adequate.
However, if you’ve got enough hiding spaces for them, even 12 light hours are Ok, especially when your tanks hold light-hungry plants too.
To create the optimal environment for cold water species, try to match your aquarium lighting to seasonal daylight hours akin to those in the temperate 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.
Light Needs for Live Aquatic Plants
While light in fish tanks is partly for your viewing pleasure, plants depend on diurnal light patterns a lot, and good quality light is paramount. (See how to choose planted aquarium lights).
However, the light used in your aquarium and the duration the light stay on will depend on the plants you have.
Some plants will thrive in low lights while others need high light for longer. Low light plants like Java moss, Java fern, and Anubias species will be fine with 8 to 10 hours of low-intensity light a day and the plants are perfect for beginners.
On the other hand, light hungry species prefer longer light hours, somewhere in the region of 12 hours a day, CO2 addition and fertilizer dosing.
That said, I also recommend you match your aquatic plants to the type of fish you have in your tank; tropical plants with tropical fish.
Ideally, keep platies, guppies, betta and cory catfish in aquariums planted with Java fern, Java moss anubias, hornwort, and Cryptocoryne.
Goldfish, minnows, ricefish, and Zebra danios come from temperate zones where daylight hours fluctuate, and are best paired with Anubias 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 12 hours a day, blue-green algae will establish exponentially.
Although it’s not just your aquarium light you should be concerned about. but also natural light from the sun. Thus, when you have your tank in a brightly-illuminated room, placing it too close to the window is not recommended.
That said, algae will probably grow in your aquarium anyway, whether too much 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, shrimp like ghost and Amano, Amano shrimp, and snails (mystery, nerite).
How to Light Your Aquarium While Away on Vacation
Most people will remember to feed their fish when leaving for vacation but fewer remember to schedule their aquarium lights for when they are away.
While some aquarists are not even sure whether to leave the lights on or off while they have a good time away from home.
Frankly, fish in your aquarium doesn’t need light to live, hence leaving the lights off is fine. If anything, leaving the lights on could be a fire hazard and will encourage algae growth.
But if you have plants in your aquarium, then you will need to leave the lights on with a timer (recommended) running a diurnal setting.
Alternatively, if your aquarium room is properly illuminated, leave the tank near a window to take advantage of the natural day-night cycle.
Heat Emitting Lights and Aquarium Temperature
This is most likely not the first thing to cross your mind, but apart from light, aquarium fixtures produce heat, meaning you’ll have to consider that when choosing the light fixtures and bulbs.
This is especially true for smaller aquariums where the possible increase in temperature can be significant.
Generally, metal halides and incadescent bulb produce a lot of heat and are therefore not the best for aquariums. Besides, incadescent technology is pretty much outdated.
The more obvious and appropriate light source would, therefore, be either LED or fluorescent, but given the two, LEDs are the harder hitter.
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 T8 fluorescent lights are not synonymous with VHO-fluorescent, which like metal halides, will spike your aquarium water temperature.
Also, T5 bulbs are preferable (as opposed to T8 and T12) because of their skinny bulbs, narrow footprint, availability, efficiency, and low heat output.
My Two Cents
Each aquarium environment is different, thus the only sure way to know how long to keep aquarium light on is trying out different setting until you find the perfect fit.
Even so, consider variables like natural and ambient lighting since every home is inherently unique.
First, think of your plants before the fish since fish tanks are less fussy about lighting. If anything, lighting a fish tanks is mostly for your own amusement.
Then do a little due diligence before buying or replacing aquarium grow lights, compare different products in the market to make sure you get the 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, seriously consider a programmable light fixture with a timer, or maybe LED night mode lights.
Enjoy Your Aquarium.