Guide
How long should an aquarium light be on
To start with, 6–8 hours of light a day is enough. Plants can't use more anyway, and every extra hour gives algae an advantage.
Updated:
Photoperiod by type of tank
| Tank | Light per day |
|---|---|
| New, first 4–6 weeks | 6 hours |
| No plants or undemanding plants | 6–8 hours |
| Planted with CO2 and fertiliser | 8–10 hours |
| Algae problem | 6 hours, while fixing the cause |
Why more isn't better
After a few hours of light plants slow down because they run short of CO2 and nutrients. Algae copes with that better, so a long photoperiod usually ends with a film on the glass and leaves. More in the guide on algae.
How to set the lighting
- Switch the light on and off at the same times every day, ideally with a timer.
- Set it to the hours when you look at the tank, e.g. 2 pm–10 pm.
- If you inject CO2, start it 1–2 hours before the light so the level has time to rise (pH and CO2).
- Fish need night: leave them a few hours of complete darkness.
- Don't rely on window light: you can't control it and it warms the water.
How Aquarium Monitor helps
The app runs the light and CO2 through smart plugs on a schedule, so the lighting hours are the same every day. The pH chart shows whether CO2 rises in time before the light comes on.
Frequently asked questions
Can I leave the aquarium light on overnight?
No. Fish need darkness to rest, and round-the-clock light feeds algae.
Does a midday light break help with algae?
Some aquarists use a break of a few hours. It may help in a tank without CO2, but shortening the total photoperiod and fixing the cause of the algae matter more.
Keep an eye on your tank from your phone
The app is free and ad-free. The monitor runs on your Raspberry Pi.