The 30-second verdict
People hear "more light = more plant growth" and run their tank 10–12 hours a day from week one. Then it turns into an algae farm and they blame the plants.
Here is the actual rule:
Light is not food. Light is the accelerator. Carbon and nutrients are the fuel. Flooring the accelerator in a tank with no fuel just spins the wheels — and algae is the smoke.
So the schedule is the opposite of most people's instinct:
- Start short — 6 hours a day, even 4 in a brand-new tank.
- Add time in tiny increments, and only when the plants are visibly growing.
- Let the plants set the pace, not the calendar and not your impatience.
- Use a timer, always — consistency matters more than the exact number.
Think of it as a balance. Every hour of light you add is weight on one side of the scale; the plants' capacity to use it is the other. Add light faster than the plants can grow into it, and the surplus goes to algae. The whole skill is keeping the two sides level.
Why this works: the balance, in plain terms
Plants photosynthesise using three things together: light, carbon (CO2), and nutrients. They can only grow as fast as the scarcest of the three allows. Give a plant more light but no more carbon, and it cannot use the extra light — it just sits there, lit up, at the same growth rate.
Algae, meanwhile, is far less fussy. It thrives on exactly that surplus — the light the plants could not use, and the nutrients they did not take up. So an over-lit tank is not "too bright for the plants." It is a tank where the plants are maxed out and everything extra is feeding algae instead.
Which gives you the lever: keep light slightly behind what the plants can handle, and there is no surplus for algae. Increase it only as the plants prove they can use more. The plants lead; the light follows.
The nutrient and CO2 side of this is covered in Planted Tank Lighting and CO2. This article is specifically about the time dimension — how many hours, and how to change them.
The schedule
A low-tech, no-CO2 tank — which is what most beginners should start with (why). Treat these as starting points, not laws:
| Stage | Photoperiod | What you are doing |
|---|---|---|
| Week 1–2 (new tank) | 4–6 hours | The tank is immature, plants are adjusting, and there are no established plants to consume nutrients yet. Short light starves early algae. Expect diatoms regardless — that is normal. |
| Week 3–4 | 6 hours | Hold steady. Watch for the first genuinely new leaves — that is the plants saying they have settled. |
| Month 2 onward | Add 30 min at a time | Once plants are clearly growing, increase by half an hour. Wait 1–2 weeks and watch before adding more. |
| Mature, thriving tank | 7–9 hours | The ceiling for most low-tech tanks. Beyond this you usually need CO2 to justify the light, or you just grow algae. |
The core discipline: the frequency of increases should be as low as possible. Add 30 minutes, then wait a fortnight and read the tank before touching it again. Nobody knows their tank's exact right number in advance — not even for their own tank. You find it by creeping up slowly and stopping when algae first appears.
Reading the tank: when to push, when to pull back
| What you see | What it means | Do |
|---|---|---|
| New leaves, healthy colour, no algae | Plants have capacity to spare | You may add 30 min — or just enjoy it |
| Green dust or hair algae appearing | Light is now ahead of the plants | Pull back 30–60 min. Do not add fertiliser to "catch up" unless you also add CO2 |
| Plants leggy, stretching upward, pale | Not enough light (or intensity), reaching for it | A modest increase is warranted |
| Black beard algae on edges and flow | Unstable CO2 — a time problem only indirectly | Stabilise conditions; do not just cut light. Which algae means what |
| Diatoms (brown dust), new tank | Immature tank, not a light problem | Wait it out. It passes on its own |
The single most useful habit: when algae appears, reduce light before you reach for any bottle. Cutting the photoperiod costs nothing and fixes the most common cause directly. Adding chemicals to an over-lit tank usually makes it worse.
The siesta method (optional)
A trick worth knowing: instead of one long block, split the photoperiod into two — for example 4 hours on, a 3–4 hour break, then 4 hours on again.
The theory is that the midday break lets CO2 levels recover (in a low-tech tank, CO2 is depleted by midday), giving plants a fresh start in the afternoon while denying algae the uninterrupted light it prefers. Results are debated, but many low-tech keepers find it helps — and it costs nothing to try, because a timer with two on/off pairs does it automatically.
It has a side benefit in this country: the second block can be scheduled for the evening, which keeps light-driven heat out of the tank during the hottest part of a UAE afternoon.
The UAE angle: two ways the climate changes the maths
1. Direct sunlight breaks the whole system. Everything above assumes you control the light with a timer. A window that hits the tank for even an hour is a second, far stronger light running on the sun's schedule, not yours — and it is the single biggest cause of unbeatable algae here. No photoperiod discipline survives it. The tank must be out of direct sun: tank placement in a Dubai flat.
2. Your light is also a heater. A fixture sitting on a closed lid dumps real heat into the water, and in a UAE summer you are already fighting temperature and the oxygen problem that comes with it. Two implications:
- A shorter photoperiod in summer is not just algae control — it is heat control. Fewer light-hours is fewer heat-hours.
- Run the lights in the evening, when the room is coolest and the AC is doing least, rather than through the 45 °C afternoon.
The heat-and-oxygen background: How to cool an aquarium in a UAE summer.
Common questions
How many hours should my planted tank get? Start at 6, end somewhere between 7 and 9 for a low-tech tank, and let the plants and algae tell you where in that range your tank sits. There is no single right number — it depends on your light, your plants and your nutrients.
Can I just leave the light on all day? No. Beyond about 9–10 hours you are almost certainly feeding algae, adding heat, and stressing fish that have no dark period. Plants do not benefit from light they cannot use.
Do fish need darkness? Yes. Fish need a day/night cycle to rest, and a consistent one reduces stress. A timer gives them that; leaving it to whenever you remember does not.
My tank gets algae no matter what I do. Check three things in order: is direct sunlight hitting it; is the photoperiod under 8 hours; and are you topping up evaporation with tap water (which concentrates nutrients over a summer). In this country those three cause most "unsolvable" algae. The full algae guide.
What is the one habit that matters most? Put the light on a timer, start low, and raise it in 30-minute steps no more than once a fortnight. Patience with the photoperiod prevents more algae than any product ever cured.