How long should aquarium lights stay on daily?
Written by
Wang Jiahao
Reviewed by
Prof. Henry Webster, Ph.D.How long you run the lights in your aquarium ultimately comes down to the individual aquarium ecosystem you are running. A fish-only aquarium requires some lights, whereas a planted one needs much more. However, the timing of that light is critical to prevent algae growth and to keep your fish and invertebrates alive and healthy. Experience has taught me, with many ups and downs, the balance of importance that lies with the number of hours the lights are on.
Fish-Only Tanks
- Maximum 6 hours daily of light exposure
- Use basic white LEDs or fluorescent bulbs
- Include a consistent dark period for fish rest
- Extend by 1 hour if displaying vibrant fish colors
Planted Aquariums
- Low-tech: 8 hours with 4-hour midday break
- High-tech: 10 hours with CO₂ injection
- Position lights 12 inches above water surface
- Reduce duration if plants show melting signs
Lights should be adjusted as soon as algae appears; reduce the duration by 1-2 hours for all tanks. For major outbreaks, the tank can be covered with blackout cloth for a safe 4 days. After this period, the lights can be increased slowly over 2 weeks to avoid shocking plants or fish.
Balance duration with light intensity. High-powered LEDs have much shorter durations than fluorescent bulbs. Position lights 6 inches or more above the water surface for shallow tanks and 12 inches above the water surface for deeper aquariums. Check your PAR values monthly to ensure your light intensity matches your expectations.
Utilize timers consistently to maintain a stable photoperiod. Random changes to light periods can introduce stress to fish and plants. I use my timers to simulate sunrise/sunset with 30-minute periods around the light schedule. Timers should also be checked monthly to ensure they are accurately set and functioning properly. Consistent schedules will lessen algae growth.
Observe plant and algae responses every week. Healthy plants indicate the lighting is correct. If there are algae problems, cut back the time immediately. Test water parameters, as incorrect nutrient levels can affect light tolerability. Make adjustments gradually, allowing at least 2 weeks between each adjustment.
Read the full article: Comprehensive Fish Tank Algae Control Guide
