Reef Tank Lighting Schedule: How Long to Run Marine Tank Lights

A good reef tank lighting schedule gives marine tank lights 8–10 hours a day in total: about a one-hour ramp-up, six to eight hours at peak intensity, a one-hour ramp-down and optional low moonlights. Corals need consistency more than long days. Running lights for 12 hours or more mainly feeds algae.

This guide explains why the photoperiod matters, gives a sample schedule you can copy into your LED app, lists PAR targets for soft, LPS and SPS corals, and covers fish-only tanks, acclimating new lights and choosing between LED, T5 and hybrid lighting.

Updated October 2026 by the team at Natural Seawater Supplier, a Croydon, London-based supplier of live natural seawater for marine aquariums, delivering across the UK 7 days a week.

Key takeaways

• Run reef lights for 8–10 hours in total, with 6–8 hours at peak intensity and ramps at each end.
• Approximate PAR targets: soft corals 50–150, LPS 75–200 and SPS 200–350 µmol/m²/s at the coral.
• Start new lights at 30–50% of the intensity you plan to use and raise it by about 5% a week over four to eight weeks.
• Fish-only marine tanks need only 6–8 hours of moderate light a day.
• Lighting alone rarely causes algae, but long photoperiods plus excess nitrate and phosphate almost always do.

What is photoperiodism and why does it matter?

Photoperiodism is the way living things respond to the length of day and night. On a coral reef, close to the equator, daylight lasts around 12 hours all year, but the sun is only strong enough to drive peak photosynthesis for several hours either side of midday. Fish, corals and invertebrates time their feeding, rest, colour and even spawning by that steady rhythm.

Most reef-building corals depend on light because tiny algae called zooxanthellae live in their tissue and photosynthesise, sharing food with the coral. As NOAA’s corals tutorial on zooxanthellae explains, that is why reef corals need clear, sunlit water. Your aquarium lighting replaces the sun, so the schedule should mimic a reef day: gentle dawn, strong midday, gentle dusk, then darkness. An erratic or overly long photoperiod stresses fish and corals and can make disease more likely.

Sample reef tank lighting schedule

Set the schedule for when you will actually be home to enjoy the tank. Many UK hobbyists run lights from late morning to late evening, for example:

That gives about 10 hours of light, 7 of them at peak. A popular alternative for SPS tanks is the “1-8-1” pattern: one hour up, eight at peak, one down. Keep moonlights very dim and switch them off after a couple of hours; a fully dark night matters for coral and fish rest.

How long should you leave aquarium lights on in a saltwater tank?

PAR (photosynthetically active radiation, in µmol/m²/s) is the useful measure of light at the coral. Figures above are hobby consensus starting points; corals in your tank may prefer a little more or less. Many local fish shops and reef clubs will lend or rent a PAR meter, which is far more reliable than a manufacturer’s chart.

Lighting a fish-only marine tank

Fish do not need intense light. In a fish-only or FOWLR tank, 6–8 hours of moderate light is plenty and keeps algae down. A cheaper marine LED with blue and white channels is fine; the money saved on lighting is better spent on a larger tank. See our saltwater aquarium for beginners guide for choosing between fish-only and reef systems.

LED vs T5 vs hybrid marine tank lights

As of 2026, widely sold reef LEDs in the UK include the AI Hydra 32 HD, Red Sea ReefLED 90 and 160S, EcoTech Radion G6 and Kessil A360X. Single fixtures such as the Hydra 32 HD and ReefLED 90 sell for around £390–£400, typically covering a 60 cm square footprint; larger tanks need two or more. Ageing fluorescent tubes are a classic hidden cause of problems: a tube still glowing after two years has changed colour and lost much of its output, and simply replacing it can transform a tank.

How to acclimate corals to new lights

1. Set the new light to 30–50% of your planned intensity, or lower if moving from old T5s to strong LEDs.
2. Keep the photoperiod at your normal length; reduce intensity, not hours.
3. Raise intensity by about 5% a week over four to eight weeks.
4. Watch the corals: bleaching tips or closed polyps mean too much; stretching, browning or reaching mean too little.
5. Place new corals low in the tank first and move them up over a few weeks.

Light drives coral growth, which uses calcium and alkalinity; keep both stable with weekly testing using our marine tank water parameters guide. Planning lighting as part of a new build? Our reef tank setup guide covers when to switch lights on during cycling.

Does lighting cause algae in a reef tank?

Light is the fuel, but nutrients are the food. Algae needs both, so the fix is usually twofold: shorten an over-long photoperiod to 8–10 hours, and bring down nitrate and phosphate with good nutrient export. Strong white light for 12 hours or more is a common trigger for green hair algae in a reef tank. For a full plan, see how to get rid of algae in a saltwater tank.

Water quality matters as much as the light. Natural seawater arrives with near-zero nitrate (0–0.9 ppm) and phosphate (0–0.05 ppm), so water changes dilute nutrients rather than add them. New customers can try 25 litres of natural seawater free.

Frequently asked questions

How long should reef tank lights be on?

Reef tank lights should be on for 8 to 10 hours a day, including about an hour of ramp-up and an hour of ramp-down, with 6 to 8 hours at peak intensity. Longer days rarely help corals and often encourage algae.

How long should you leave aquarium lights on in a saltwater fish only tank?

A fish only saltwater tank needs about 6 to 8 hours of light a day. Fish do not need intense light, and a shorter photoperiod helps keep algae under control.

Should I turn off aquarium lights at night?

Yes. Fish and corals need a dark period every night to rest. Dim moonlights for an hour or two after the main lights are fine, but switch everything off for the rest of the night.

What PAR do soft corals, LPS and SPS need?

As a starting point, soft corals do well at about 50 to 150 PAR, LPS at 75 to 200 and SPS at 200 to 350 PAR. Measure with a PAR meter and adjust to how your corals respond.

Do blue lights cause algae in a marine tank?

Blue light on its own rarely causes algae. Algae is driven by long photoperiods combined with excess nitrate and phosphate, so check both your schedule and your nutrient levels.

How often should T5 bulbs be replaced?

Replace T5 tubes every 9 to 12 months. Their output and colour shift as they age even though they still light up, which can slow coral growth and encourage algae.

Bottom line

Keep your reef tank lighting schedule simple and steady: 8–10 hours a day with gentle ramps, peak PAR matched to the corals you keep, and any change made gradually. Combine that with low nutrients and your marine tank lights will grow colourful corals rather than algae.

Sources

External sources cited in this article (checked October 2026):

• Corals tutorial on zooxanthellae (NOAA)