Aquarium Light Duration Calculator

How This Tool Works

This calculator determines the optimal lighting duration based on your plant type and tank depth. Different aquatic plants have varying light requirements - low light plants (like Java fern, Anubias) need less intense and shorter duration lighting, while high light plants (like carpeting plants, red plants) require longer, more intense lighting periods. Tank depth also matters because light intensity decreases as it travels through water, so deeper tanks need longer lighting periods to ensure adequate light reaches plants at the bottom.

Proper lighting duration is crucial for plant health and algae control. Too little light stunts plant growth and can cause plants to die, while too much light promotes excessive algae growth. Most planted aquariums benefit from 6-10 hours of light per day, with a consistent schedule maintained using a timer. This mimics natural day/night cycles and helps maintain a healthy balance between plant growth and algae control.

Lighting Duration Guidelines

• Low Light Plants: 6-8 hours daily - includes Java fern, Anubias, Cryptocoryne, mosses
• Medium Light Plants: 8-10 hours daily - includes most stem plants, swords, most carpeting plants
• High Light Plants: 10-12 hours daily - includes red plants, demanding carpeting plants, CO2-dependent species
• Shallow Tanks (<30cm): Standard duration - light penetrates easily
• Medium Tanks (30-50cm): Add 1-2 hours - light needs more time to reach bottom
• Deep Tanks (>50cm): Add 2-3 hours - significant light loss requires longer duration
• Algae Control: If experiencing algae issues, reduce lighting by 1-2 hours

Lighting Best Practices

• Use a Timer: Always use an automatic timer to maintain consistent lighting schedules
• Gradual On/Off: Some LED systems offer sunrise/sunset modes to reduce stress on fish
• Consistent Schedule: Maintain the same lighting hours daily - plants and fish adapt to routines
• Monitor Algae: If algae grows excessively, reduce lighting duration by 1-2 hours
• Light Intensity: Duration and intensity work together - high intensity may need shorter duration
• Break Period: Some aquarists use a 4-6 hour "siesta" break to reduce algae (e.g., 4 hours on, 4 off, 4 on)
• New Tanks: Start with 6 hours and gradually increase to prevent algae blooms in new setups
• CO2 Injection: High light setups often require CO2 injection for optimal plant growth

FAQ

• How long should aquarium lights be on?
  Most planted aquariums need 6-10 hours of light per day, depending on plant requirements and tank depth. Low light plants (Java fern, Anubias) need 6-8 hours. Medium light plants (most stem plants) need 8-10 hours. High light plants (red plants, demanding carpets) may need 10-12 hours. Deeper tanks (over 50cm) may need 1-3 additional hours to ensure adequate light penetration. Always start with less and increase gradually while monitoring for algae growth.
• Can I leave aquarium lights on too long?
  Yes, excessive lighting (12+ hours) can cause significant algae problems, stress fish, and waste electricity. Most aquariums don't need more than 10-12 hours even for high light plants. It's best to use a timer to maintain consistent lighting schedules and give plants and fish a natural day/night cycle. Fish need darkness to rest, and plants also benefit from a dark period. If you're experiencing algae issues, reducing lighting duration is often the first solution to try.
• Should I use a lighting schedule with breaks?
  Some aquarists use a "siesta" schedule (e.g., 4 hours on, 4 hours off, 4 hours on) to reduce algae while maintaining plant growth. This can help control algae in high light setups. However, it's not necessary for most aquariums. A continuous 6-10 hour period works well for most setups. If you're struggling with algae, try the siesta method, but ensure your total daily light hours still meet your plants' needs.
• How does tank depth affect lighting needs?
  Tank depth significantly affects light penetration. Light intensity decreases as it travels through water - approximately 50% reduction every 30cm of depth. Shallow tanks (under 30cm) need standard lighting duration. Medium tanks (30-50cm) may need 1-2 additional hours. Deep tanks (over 50cm) often need 2-3 extra hours or more powerful lights to ensure adequate light reaches bottom-dwelling plants. Deeper tanks may also benefit from more intense lighting systems.
• What if I have algae problems?
  If experiencing algae issues, first reduce lighting duration by 1-2 hours. Also check: Are you overfeeding? Excess nutrients fuel algae. Are you doing regular water changes? Clean water helps. Is your lighting too intense? Consider dimming or raising lights. Are you providing enough CO2? Plants need CO2 to outcompete algae. Reduce lighting duration first, then address other factors. Most algae problems can be solved by reducing light and improving maintenance.
• Do I need special lights for planted aquariums?
  While standard aquarium lights can work for low light plants, dedicated plant lights (full spectrum LEDs, T5/T8 plant bulbs) provide better results. Plant lights emit wavelengths that plants use for photosynthesis (red and blue spectrum). For high light plants, you'll need more powerful, specialized lighting. LED lights are popular for their efficiency, low heat, and customizable spectrum. Research your plants' specific light requirements and choose appropriate lighting intensity and spectrum.