We are reader supported. When you purchase through links on our site, we may earn an affiliate commission. Also, as an Amazon affiliate, we earn from qualifying purchases.
Finding the right daily lighting schedule is one of the simplest ways to keep your aquarium healthy. Too little light, and plants and corals struggle. Too much light, and algae explodes while fish become stressed. In this guide, you will learn how many hours aquarium lights should be on for different setups, how to adjust the schedule based on what you see, and how to use timers to make your routine easy and consistent. The goal is to help you set a light duration that supports life in your tank without inviting algae problems.
Why Light Duration Matters
The role of light in aquatic ecosystems
Light drives photosynthesis. In planted freshwater tanks and reef aquariums, plants, macroalgae, and corals use light to make energy and grow. Fish do not need light to eat or survive in the same way, but they do use light to know when to be active and when to rest. The right duration supports healthy growth for photosynthetic life while giving fish calm, dark periods to rest.
Circadian rhythm and fish stress
Fish rely on a day–night cycle. When lights stay on for too long, fish may hide more, lose color, or become aggressive. When lights turn on and off at random times, fish may feel unsafe. A steady schedule lowers stress, improves feeding responses, and helps your aquarium community behave naturally.
Light and algae balance
Algae thrives when it gets long hours of light and excess nutrients. If nutrients are high or plants are weak, even a normal photoperiod can trigger algae. Getting the duration right is a powerful way to reduce algae without harsh chemicals. Most tanks do well with 6–10 hours of full light per day, depending on the setup and intensity.
General Rules of Thumb
Quick guidelines by tank type
Freshwater fish-only or low-light plants: 6–8 hours of full light.
Freshwater planted (low to medium light, no CO2): 7–8 hours of full light.
Freshwater planted (medium to high light with CO2): 8–10 hours of full light, adjusted to plant response and algae control.
Saltwater fish-only (FOWLR): 6–8 hours for viewing; the tank does not need long hours of bright white light.
Reef with corals: 8–10 hours total, often with 6–8 hours of high-intensity “daylight” and extra blue-only time at the edges for color and viewing.
What if your room gets daylight?
Ambient daylight counts. If your tank sits near a window, it may get hours of indirect light even when the aquarium light is off. In that case, shorten the artificial photoperiod by 1–2 hours. Direct sun can overheat the tank and fuel algae. Use curtains or move the tank if sun hits the glass.
Signs your photoperiod is wrong
Too long: green dust or film algae on glass each day, hair algae on decor, brown diatoms lingering after the first 1–2 months, fish hiding more, corals retracting by day.
Too short: plants become leggy and pale, red plants lose color, corals lose extension, fish seem lethargic during the light period, you rarely see your tank fully lit when you are home.
Freshwater Community Tanks
Fish-only or low-light planted
For tanks with hardy plants like Anubias, Java fern, or moss, keep the light on for 6–8 hours. These plants do not need intense light. Long photoperiods usually invite algae before plants benefit. Start at 7 hours and adjust by 30 minutes per week as needed.
Suggested schedule and timing
Set the light to turn on when you are home to enjoy the tank. For example, 2:00 pm to 9:00 pm works well for many people. Your fish will adapt to your schedule. Consistency matters more than the exact hour.
Dealing with algae and ambient light
If green film returns to the front glass every day, lower the photoperiod by 30–60 minutes, reduce feeding slightly, and clean the filter if it is due. Check if the room light or window is adding hours of brightness. If your light is very strong, dim it or raise it, rather than only shortening the hours.
Nighttime viewing and blue “moonlight”
Many lights include blue night LEDs. Using them all night is not recommended. Constant light can disturb fish rest and encourage algae. If you enjoy evening viewing, set blue light for 30–60 minutes after the main light turns off, then complete darkness until the next day.
Planted Aquariums
Match hours to plant type and CO2
The more light and CO2 you provide, the more hours you can usually run, but the balance between light, CO2, and nutrients is critical. Plants need enough light to use the CO2 and fertilizers you add. Extra light without enough CO2 or nutrients leads to algae.
No CO2 added: 7–8 hours of moderate intensity is a safe range.
Low-tech with liquid carbon: 7–8.5 hours if growth is steady and algae is controlled.
Pressurized CO2: 8–10 hours is common, with CO2 starting 1–2 hours before lights on and ending 1 hour before lights off.
Low, medium, and high light plants
Low-light plants (e.g., Anubias, Java fern, Cryptocoryne) are fine at 7–8 hours. They can be shaded by floating plants or hardscape.
Medium-light plants (e.g., many stem plants, dwarf sag, hydrocotyle) often like 8 hours if CO2 and nutrients are balanced.
High-light plants (e.g., carpeting plants like Monte Carlo, Glossostigma, or colorful stems) need strong intensity and stable CO2; 8–10 hours can work, but only if CO2 is steady and nutrients are adequate.
Fertilizer and CO2 coordination
Run CO2 early: start 1–2 hours before the light so the water reaches target CO2 when the light turns on. End CO2 about 1 hour before lights off to avoid waste. Dose fertilizers consistently to match plant growth. If new algae appears, reduce the photoperiod by 30–45 minutes and check CO2 stability before changing nutrients.
Siesta method and ramping
A “siesta” splits your daily light into two periods with a mid-day break. Example: 4 hours on, 2 hours off, 4 hours on. This can limit algae in some cases by giving plants time to process nutrients. It helps more in low-tech tanks with moderate light than in high-CO2 setups. Try it if you see algae despite careful feeding and maintenance.
Ramping simulates sunrise and sunset and reduces fish stress. Many LED fixtures allow a 15–60 minute ramp up and ramp down. Ramping does not replace a proper photoperiod. For example, you might have a 45-minute ramp up, 7.5 hours at full power, and a 45-minute ramp down.
Saltwater Tanks
Fish-only (FOWLR) setups
Fish-only saltwater tanks do not need long hours of strong white light. Run 6–8 hours for viewing. Blues can be used slightly longer if you enjoy the look, but keep total light reasonable to limit algae on rock and glass.
Reef tanks with corals
Corals contain symbiotic algae (zooxanthellae) that need light to produce energy. Most reef tanks do well with 8–10 hours total. A common pattern includes a longer blue period with a shorter high-intensity white period in the middle.
Example breakdown: 2 hours blue ramp, 6–8 hours full spectrum at target intensity, 2 hours blue ramp down. The “whites” or broad-spectrum period is when most photosynthesis occurs. The blue-only periods improve viewing and coral fluorescence without blasting the tank with extra intensity.
Blue vs. white channels
Blue wavelengths penetrate water well and are critical for coral growth and color. Whites add balance and render color more naturally. Do not push white intensity too high to avoid bleaching. If you see corals pale or retract, reduce intensity first before changing duration. If algae on glass grows daily, consider trimming the total time by 30–60 minutes.
Acclimating corals to light
When adding new corals or upgrading to a stronger light, reduce intensity and/or duration for 1–2 weeks and increase slowly. Start at 50–70% intensity and a shorter day (for example, 7–8 hours total). Move corals higher or increase light only after they show normal extension and color.
Special Situations
New tanks and the “ugly phase”
During the first 4–8 weeks, many aquariums go through diatoms and then green algae as the system matures. Shorter light durations help. Start at 6 hours for fish-only and 6.5–7 hours for planted or reef tanks, then add 30 minutes per week as the tank stabilizes. Clean the glass regularly, keep filters maintained, and avoid overfeeding.
Tanks with floating plants or tannins
Floating plants like Salvinia or frogbit shade the water and reduce effective light intensity. With dense floaters you can run a slightly longer photoperiod, but it is often better to thin them so the whole tank gets even light. In blackwater tanks with tannins, light is dimmer; plants may need longer hours, but fish often prefer subdued lighting. Strike a balance based on plant response and algae presence.
Deep tanks and intensity versus duration
In tall aquariums, light loses strength with depth. Increasing duration cannot fully replace missing intensity. If plants or corals near the bottom struggle, increase intensity or move them higher rather than pushing to very long hours. Very long photoperiods often grow algae without solving the core issue.
Breeding, nocturnal fish, and moonlight
Some species breed seasonally with changing day length. You can extend or shorten the photoperiod by 30–60 minutes over a few weeks to simulate seasons, but do this gently. For nocturnal fish like many catfish, ensure they have a long, dark period and dim hiding areas during the day. Use “moonlight” only for short viewing windows; leave it off most of the night so fish rest.
Tools and Techniques to Get It Right
Timers and smart plugs
Consistency is the most important factor. Use a mechanical or digital timer, or a smart plug you can control from your phone. Set the schedule once, and let the timer do the work. Many aquarium lights have built-in programming; use the simplest schedule that matches your goals.
Dimmers and dawn/dusk effects
A dimmer or programmable ramp reduces sudden changes and keeps fish calm. Even a 15–30 minute ramp is helpful. If your fixture does not ramp, turn on a room light for a few minutes before the tank light, and turn the room light off a few minutes after, to soften transitions.
Measuring light simply
If you grow demanding plants or corals, knowing PAR (photosynthetically active radiation) at different depths is valuable. Entry-level PAR meters can be borrowed or rented, but you can also use common reference points and plant response. Healthy, compact plant growth and coral polyp extension are good signs. If growth is weak at the bottom, increase intensity slightly or move organisms higher before extending duration.
Maintenance habits that support a stable photoperiod
Clean the light’s splash guard or lens monthly; salt creep and mineral deposits reduce output and change spectrum. Keep the lid or glass top clear. Maintain filters and perform regular water changes to keep nutrients in check. Good maintenance allows you to run a normal photoperiod without waking up to algae blooms.
Example Schedules You Can Copy
Freshwater fish-only or low-light planted
Lights on: 2:00 pm — Lights off: 9:00 pm (7 hours). If algae appears, change to 2:30 pm to 8:30 pm (6 hours). If plants look weak but algae is under control, try 2:00 pm to 9:30 pm (7.5 hours).
Low-tech planted, no CO2
Ramp up: 30 minutes from 1:30 pm. Full power: 2:00 pm to 9:30 pm (7.5 hours). Ramp down: 30 minutes to 10:00 pm. If algae grows, reduce full power by 30 minutes.
High-tech planted with CO2
CO2 on: 12:00 pm. Lights ramp up: 1:00 pm. Full power: 1:30 pm to 9:30 pm (8 hours). CO2 off: 8:30 pm. Lights ramp down: 9:30 pm to 10:00 pm. Adjust intensity first if plants struggle, then adjust duration in 15–30 minute steps.
Saltwater FOWLR
Blue ramp: 12:00 pm to 1:00 pm. Daylight: 1:00 pm to 7:00 pm (6 hours). Blue ramp down: 7:00 pm to 8:00 pm. Total 8 hours of light with 6 hours bright viewing.
Mixed reef
Blues on low: 11:00 am. Ramp to target: until 1:00 pm. Full spectrum peak: 1:00 pm to 8:00 pm (7 hours). Blue-only down-ramp: 8:00 pm to 10:00 pm. Total photoperiod about 11 hours with 7-hour peak. If algae increases, trim the blue-only periods before trimming the peak, unless corals show stress.
How to Adjust Your Photoperiod
Use small steps and observe for a week
Make one change at a time. Reduce or increase by 15–30 minutes and watch for 7–10 days. Look at glass algae, plant growth tips, coral extension, and fish behavior. Patience avoids ping-ponging between problems.
Prioritize intensity before duration with strong lights
If you run a powerful LED over a small tank, dimming often solves algae faster than cutting hours. Very short days with very high intensity can still trigger algae and stress. Aim for moderate intensity with a moderate day length.
Coordinate feeding and maintenance
Extra nutrients plus long light equals algae. If you increase feeding, increase plant mass or reduce light slightly. After filter cleaning or large water changes, algae often eases, letting you maintain a steady photoperiod.
Frequently Asked Questions
Is leaving aquarium lights on 24/7 ever okay?
No. Fish and invertebrates need darkness to rest. Photosynthetic life needs a daily rhythm. Constant light causes stress, poor health, and algae blooms. Keep a dark period of at least 12 hours for most home tanks.
Can I split the light into morning and evening sessions?
Yes. A split photoperiod can work, especially if you want to view the tank at breakfast and in the evening. For example, 8:00 am to 12:00 pm, off during work, then 6:00 pm to 10:00 pm. Plants and fish usually adapt. Watch algae; if it increases, shorten one block or reduce intensity.
Do moonlights bother fish?
Short, dim blue periods for viewing are fine. All-night lighting is not ideal. Use 30–60 minutes after lights off if you enjoy it, then complete darkness.
How long until changes make a difference?
Algae on glass responds within days. Plant health and coral color respond over 2–4 weeks. Make small adjustments, then wait at least a week before the next change.
Is longer always better for plant growth?
No. Plants need enough light intensity and nutrients. When intensity is low, longer hours help a little, but going beyond 9–10 hours usually encourages algae more than plant growth. Improve intensity and nutrient balance before stretching hours too far.
Practical Tips for Beginners
Start conservative and increase slowly
Begin with the lower end of the recommended range for your tank type. Increase by 15–30 minutes only when growth is healthy and algae is controlled. It is easier to add light than to fight an algae bloom.
Pick viewing hours that fit your life
You will enjoy your aquarium more if the lights are on when you are home. Set the start time later in the day if you work mornings. Fish adapt to your schedule as long as it is consistent.
Use covers and place the tank wisely
Avoid direct sunlight. If sunlight is unavoidable, reduce the photoperiod and consider a background or blinds. Keep the light fixture clean and protected from splashes to maintain output and spectrum.
Keep records
Write down your light hours, intensity settings, fertilizer doses, and any algae or growth changes. Notes help you learn your tank’s personality and make better decisions over time.
Troubleshooting by Symptom
Green film algae every day
Reduce photoperiod by 30 minutes, clean glass, and check feeding and filters. If it persists, reduce intensity 10–20% and review nutrient levels.
Brown diatoms in a new tank
Normal in the first 1–2 months. Keep the photoperiod short (6–7 hours), clean surfaces, and maintain the filter. Diatoms fade as the tank matures.
Hair or fuzz algae on plants
Lower light duration by 30–60 minutes, improve flow, and ensure CO2 is stable if used. Remove affected leaves and keep nutrients balanced rather than zeroing them out.
Plants pale or not growing
If algae is low, increase duration by 15–30 minutes or raise intensity slightly. Ensure macronutrients and micronutrients are dosed, and confirm CO2 delivery if running high light.
Corals receding or bleaching
Reduce intensity first by 10–20%. If needed, shorten the peak period by 30 minutes. Check for stable alkalinity, calcium, magnesium, and nutrients. Re-acclimate new corals slowly.
Putting It All Together
Balanced photoperiod strategy
1) Choose a starting duration based on your tank type. 2) Keep the schedule consistent with a timer. 3) Watch plant, coral, and fish responses for a week. 4) Adjust in small steps. 5) Fix intensity and maintenance issues before adding hours. This method keeps your aquarium stable and attractive with minimal effort.
Conclusion
The best daily lighting duration for your aquarium depends on what lives in the tank, how strong your light is, and how much natural light the room provides. As a simple starting point, aim for 6–8 hours in fish-only and low-light freshwater tanks, 7–10 hours in planted aquariums depending on CO2 and plant demand, and about 8–10 hours in reef tanks with a shorter high-intensity peak. Use timers for consistency, ramp lights to reduce stress, and tune duration in small steps based on algae growth and the health of your plants or corals. With a balanced photoperiod, your fish will be calmer, your plants and corals will thrive, and your tank will be a joy to view every day.