How long should aquarium lights be on? Can you leave them on all day, or will the act disturb the aquatic species in your tanks?
To answer your question, you can keep the tank lit for 8 to 12 hours a day. However, don’t forget that there are several factors that can influence how long you can keep aquarium lights on.
Please keep reading to learn more as we “shed light” on this pressing issue.
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How Long Should I Keep My Aquarium Lit?
A question of many beginner aquarists is how many hours of light do fish need?
The standard recommendation is eight to twelve hours daily. However, it would be best to start with eight hours and note any change in fish tank parameters, then you can make adjustments to the schedule based on your observation.
For instance, you can leave fish tank light on for 8 hours daily for a month and observe algae growth, particularly their color.
Too many nutrients in the aquarium water and light exposure longer than necessary will turn the fish tank water yellowish to brownish from excessive green algae growth. Hence, it makes sense to reduce the hours the aquarium lights are on.
On the other hand, brown algae in fish tanks often indicate insufficient light and too many nutrients. You can leave the fish tank lights on for longer hours or install brighter illumination in the aquarium.
Hence, you can decide on the most appropriate fish tank illumination pattern (i.e., 10 hours on and 14 hours off/12 hours on and off) for your needs. It takes time, but you will eventually find the sweet spot.
Does Fish Type Impact Aquarium Lighting Requirements?
Experts say fish do not have a physiological or biological need for illumination. Translated into layman’s terms, fish do not care if they get light or not. The aquarium light schedule aquarists observe is purely for people.
However, part of being a responsible aquarium hobbyist is knowing your fish, especially their behavior in their natural habitat.
Although most fish do not mind having eight to twelve hours of light during the day, illumination will benefit them more if you learn their natural light requirements.
1. Tropical freshwater fish
For instance, Bettas, Rainbowfish, Angelfish, Guppies, and other tropical freshwater fish can tolerate longer light exposures (about 12 hours daily) than other species. The 12-hour freshwater aquarium light on/off schedule mimics these species’ natural habitats.
However, some tropical fish (i.e., Cichlids and Tetras) require little light exposure. Eight to nine hours of daily illumination is sufficient for these species.
2. Coldwater fish
Freshwater fish living in colder environments require less light exposure.
It is worth noting that cold regions have shorter daylights than night darkness, especially in winter. Hence, eight hours is sufficient for Goldfish, Zebra danios, Minnows, Koi, and Hillstream loaches.
However, we recommend adjusting the illumination times according to the changing of the seasons. For instance, 6 hours might be a good idea in the winter, while 10 hours are sufficient in the summer.
3. Saltwater fish
Saltwater fish species require about eight to ten hours of light daily. They have a diurnal (daytime) pattern similar to the real world (their natural habitat).
You can leave aquarium light on from eight in the morning to four or six in the late afternoon/evening. Your Filefish, Snowflake moray, Maroon Clownfish, Pufferfish, and Marine Wrass will love this schedule.
4. Fish in reef tanks
Aquatic life forms in reef systems vary in illumination requirements compared to their deeper-sea counterparts. Sea anemones, corals, and other reef ecosystem elements are closer to the water’s surface, absorbing more light from the sky.
Hence, ten to twelve hours of light exposure, including fish, is necessary for these reef elements. Reef fish species, anemones, and corals also require blue or cool white light.
The following table summarizes the illumination length requirements of different fish species according to type.
Fish Type according to Aquarium Setup
|Recommended Hours of Light per Day
8 to 10
10 to 12
Sample Fish Species
On a side note, the best time to turn on aquarium light depends on your preferences. Most aquarists turn the fish tank lights on during the daytime to mimic fish’s natural water environment in the wild.
Depend on Size of Fish Tank and Stocking Capacity
How many fish living in your aquarium also matters. For example, a community tank requires 12 hours of illumination because its inhabitants have diverse behavioral patterns.
It allows fish to feed and play when there is light and rest when it is dark. It ensures fish stay healthy and happy. Fire eels, soldierfish, invertebrates, and other nocturnal aquatic creatures can also lead a happy life as their diurnal tankmates.
On that note, fish tank size also matters. Since most community tanks require larger aquariums, it is safe to assume that the larger the fish tank, the longer the aquarium light stays on (but not longer than 12 hours).
How About Other Livestock?
Some aquariums do not only feature colorful fish. They include snails, crabs, crayfish, shrimp, and other invertebrates.
These creatures do not need light to survive. However, they thrive on algae, which relies on light to survive, grow, and multiply. Hence, 10 to 11 hours of light should be enough for them.
How Long Should Fish Tank Lights Be on for Live Aquatic Plants?
Although fish are not fully dependent on light for survival, plants are. And most fish rely on plants for energy.
Plants, including aquatic varieties, need light, water, and carbon dioxide. The average aquatic plant needs at least a dozen hours of illumination from ambient room lighting or supplemental fish tank lighting.
However, as discussed in the preceding section, fish species have varying illumination requirements. The ideal setup should be to match an aquatic plant’s light requirements to those of the fish in the aquarium.
Here is a table you can consider for matching your aquatic plants to your fish’s light requirements.
Now, you do not have to worry about matching anything if your aquarium does not have any live aquatic plants.
Signs of Too Much Light and What Happens if Too Much Light in Fish Tank
You know your fish tank receives too much light if you notice the water turning yellowish or brownish, making the tank look muddy and less appealing. This color change results from an overabundance of green algae.
You might also notice the aquarium water temperature to be higher than ideal. This is because some fish tank lights produce heat that can warm the water the longer the light stays on. Examples are metal halides, incandescent bulbs, and VHO fluorescent lights.
Rising water temperatures can kill live aquatic plants and fish species. The best lighting for such purposes are LEDs and standard fluorescent lights.
Frequently Asked Questions
Is it OK to leave aquarium light on all the time?
No, it is not OK for the fish tank light be on all the time. Like us, fish need as little stimuli as possible during rest periods to allow their bodies to energize from swimming all day. Light at sleep times can stress fish.
Moreover, leaving the aquarium light on 24/7 can promote excessive algae blooms.
Should I turn aquarium lights off at night?
Yes, turning the aquarium lights off at night is always sound advice to minimize fish stress and prevent rapid algae growth.
Can fish survive in a fish tank without lights?
Yes, fish can survive in an aquarium without lights. Experts say fish biology dictates light is unnecessary for optimum functioning. However, they also add that fish require “less light” than plants to survive. Hence, “light” (although minimal) is still necessary for fish.
It is worth remembering that most fishes need light to mimic day and night, allowing them to know the time for rest and play. Goldfish need light to maintain its vibrant color. Most fish are more disease-resistant with adequate light exposure, too.
Moreover, complete darkness might make fish more lethargic and reduce their appetite.
The answer to the question of how long should aquarium lights be on varies depending on the fish tank setup. A tropical freshwater aquarium can benefit from a 12-hour daytime light schedule, while a cold water fish tank setup needs only eight hours.
Marine aquariums also vary in lighting requirements. Reef systems need longer light exposures (10 to 12 hours) than standard saltwater aquatic ecosystems (8 to 10 hours).
Algae growth, stress, and water temperature fluctuations are the principal concerns when exposing fish to excessive (or inadequate) light.