Your lights are the one piece of reef kit that never takes a day off. They shape how quickly corals grow, how their colours develop, and how much time you spend scraping green film off the glass. Get the daily cycle roughly right and almost everything else in the tank becomes easier to manage.
The good news is that a sensible schedule is not complicated. It comes down to two numbers — how bright, and for how long — plus a shape: the slow rise and fall that convinces your livestock the day is behaving normally. Here is how to put one together.
Start with the two dials: intensity and photoperiod
Intensity is how much light reaches the coral. Serious reefers measure it in PAR, but most of us work in percentages on a phone app, which is fine as long as you change things slowly and watch the tank. Photoperiod is simply how many hours the lights run each day. The two are linked: a longer photoperiod at high intensity stacks up stress in the same way as running very bright for fewer hours.
For most mixed reefs, a total photoperiod of ten to twelve hours works well, with a peak of around six to eight hours at your chosen intensity. The rest of the day is spent ramping up and down. If you keep demanding SPS corals under strong lighting, stay closer to the shorter end of that peak; a soft-coral or LPS-dominated tank will be perfectly happy with less.
The four phases of a reef day
Natural reefs do not snap from black to full sun. Replicating that shape is the single easiest improvement you can make to your lighting.
- Ramp-up (dawn): one to two hours, blue-heavy and dim. Corals open, fish wake up, and nothing gets startled.
- Peak (midday): five to seven hours at your main intensity, with whatever white/blue balance you prefer.
- Ramp-down (dusk): one to two hours, losing white first and ending in deep blue.
- Moonlight: optional, very dim, and best kept short. A faint blue glow for an hour or two is plenty; all-night moonlight tends to encourage algae and can disrupt fish resting behaviour.
A starter schedule you can copy
These clock times are a template rather than a rule — shift them to suit when you are actually home to enjoy the tank.
- 10:00 — lights on at 1 per cent, deep blue.
- 10:00–12:00 — ramp gradually to your peak settings.
- 12:00–18:00 — hold at peak. This is your six-hour window.
- 18:00–20:00 — ramp down, fading white out before blue.
- 20:00–21:30 — moonlight at 2–3 per cent.
- 21:30 — off.
Total lit time: eleven and a half hours, with six hours at peak. That is a comfortable starting point for a mixed reef, and it leaves your evening free for viewing.
Finding the right intensity without a PAR meter
Begin lower than you think you need — around half of what the fixture can do — and let the corals tell you. Over a fortnight, healthy corals show good polyp extension, steady colour and visible growth at the tips or edges. Bleaching, shrunken polyps, or tissue pulling away at the base are signs you have gone too far, too fast.
Increase in small steps: roughly 5 to 10 per cent every two weeks, then wait and watch. When you add a new coral, place it low or in a shaded spot and move it up over several weeks. Even a light-loving species straight from a supplier's tank needs time to adapt to yours.
Matching the cycle to what you keep
Corals
Soft corals and most LPS come from shallower, often turbid water and tolerate gentler light. SPS corals and clams want more intensity and tend to colour up best under a shorter, stronger peak. In a mixed tank, aquascape for it: put the high-light species near the top under the brightest part of the fixture, and let the shaded lower regions do the work of protecting the rest.
Fish
Fish care about rhythm more than brightness. Abrupt dark-to-bright transitions make them dash for cover, and they will rest more calmly if the room is not pitch black when the tank lights come on. A gentle ramp solves most of this.
Refugiums
If you run a refugium with macroalgae, light it on a reverse cycle — on at night, off during the day. It keeps photosynthesis ticking over around the clock, which helps steady pH and oxygen when the display tank is dark.
Mistakes that catch beginners out
- Changing intensity and duration at the same time, so you cannot tell which one helped.
- Running fourteen-hour photoperiods in the hope of faster growth. You usually get algae instead.
- Leaving moonlight on all night, every night.
- Switching the lights on and off by hand. Use a timer or controller — consistency matters more than any particular setting.
- Blaming lighting for an algae outbreak that is really a nutrient or flow problem.
A routine you can stick to
Write your schedule down, set it once, and then leave it alone for a fortnight. Keep a short note of what you changed and how the tank responded; a few lines in a notebook or phone note is enough. Change one variable at a time, wait two weeks, then judge.
Review the whole thing every month or two. As corals grow in, shaded areas appear, colonies start competing for space, and a setting that suited a young tank may need nudging. If you ever need to treat the tank or move rockwork around, drop the peak intensity for a week afterwards to give everything a chance to settle.
Do that, and your lighting becomes what it should be: a quiet, reliable background rhythm that lets the rest of the reef get on with growing.
Photo: sannebaan / Pixabay
