Aquarium photoperiod means the time the light is on each day. A repeatable schedule is more useful than switching it on whenever somebody wants to view the fish. For a newly planted freshwater tank, begin with a conservative period and review growth before extending it.
A starting schedule, not a rule for every aquarium
Tropica’s startup guidance uses six hours a day for the first three weeks, followed by a gradual increase towards eight hours. This is a useful planted-tank starting example, not a promise that every lamp and plant combination will work at the same setting.
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| Stage | Practical approach |
|---|---|
| New planting | Set a six-hour daily block and keep brightness conservative for the chosen plants. |
| After establishment begins | Look for healthy new leaves and manageable algae before extending the schedule. |
| If more time is needed | Make a small change, such as 30 minutes, and observe before changing anything else. |
| Stable, healthy aquarium | Keep the schedule that works. Reaching eight hours is not a target you must force. |
| Deteriorating plants or increasing algae | Hold off on extending the day and investigate the cause. |
The small-step approach above is a practical monitoring method. Plant growth rates vary, so use photographs and notes rather than a fixed deadline for improvement. A mature tank with a different setup may need a different programme.
Count the whole lighting day
Check the programme on the actual fixture. A dawn ramp, bright daytime block, evening viewing period and blue night mode can add up to a much longer day than the main timer suggests. Keep a genuine dark period. Strong window light also affects the aquarium even when the fixture is off.
Choose a block that includes your usual viewing time. For example, 15:00–21:00 is six hours; it is not intrinsically better for plants than another consistent six-hour block. Recheck the clock and programme after power interruptions instead of assuming the timer recovered correctly.
Brightness is a different decision
Photoperiod does not describe how intense the light is. If plants are shaded beneath a dense canopy, a longer day may not solve the problem. If the light is unnecessarily strong for a low-demand layout, duration is only part of the adjustment. See how to compare aquarium light output and coverage.
When injected CO2 is used, follow the equipment instructions and coordinate its operation with the lighting plan. Do not increase gas delivery simply because the light is on longer. Fish distress takes priority over plant growth or aquascaping goals.
If algae appears
- Confirm the timer is doing what you intended.
- Check direct sunlight, recent intensity changes and shading.
- Remove accumulated waste and review feeding and routine maintenance.
- Check plant condition, nutrients and circulation rather than identifying a single cause from algae alone.
- Change one controllable factor, record it and reassess.
Fertiliser is not reserved for CO2-injected tanks. Nutrient needs depend on plants, substrate, fish load and the product being used. Equally, a fixed fertiliser increase is not a treatment for every algae problem. Use our algae troubleshooting guide and plant-symptom guide to narrow the checks.
Frequently asked questions
Should I split the light into two sessions?
A split schedule can accommodate viewing time, but it is not a reliable algae cure. A single consistent block is simpler to evaluate when starting out.
Should I keep increasing the hours every week?
No. If growth is healthy and the layout is manageable, leave the schedule alone. Extra hours are not automatically an improvement.