Do LED aquarium lights cause algae growth?
Written by
Wang Jiahao
Reviewed by
Prof. Henry Webster, Ph.D.Can LED aquarium lights cause algae? The source of the light doesn't cause those algae blooms you get; it's caused by the length and/or intensity of the light reaching your tank (light GIR). LED bulbs give off less heat than incandescent bulbs. They can be controlled for the spectrum accordingly. When used properly, your plants should outcompete algae; however, problems arise when the duration and/or intensity exceed the needs of your tank.
Duration Control
- Fish-only tanks: Maximum 6 hours daily
- Low-tech planted: 8 hours with siesta period
- High-tech planted: 10 hours with CO₂ injection
- Algae outbreaks: Reduce by 2 hours immediately
Intensity Management
- Shallow tanks (<12"): 20-40 PAR sufficient
- Medium-depth: 40-80 PAR for moderate plants
- Deep planted: 80+ PAR only with CO₂ supplementation
- Dimming feature: Essential for gradual sunrise/sunset
Prevent algae by balancing light with other elements; strong light needs matching nutrient control and CO₂ injection. If not, the algae, along with the plants, will work hard to utilize that light. I rely on timers for regular photoperiods. As part of my routine, I include a 4-hour dark period each midday; this "siesta" break disrupts the algae's photosynthesis cycle.
Choose the LED spectrums wisely; avoid pure cool white bulbs with a color temperature above 6500K. It's best to have a blend of warm white + red/blue channels. This allows for healthy plant growth without promoting algae growth. Full-spectrum LEDs are best, and any temperature between 5000 K and 6500 K will work well. Be sure to acclimate your plants to the increased light over two weeks.
Watch your tank closely after adjusting the lighting. The 72-hour bubble rule also applies to the glass. If you see algae growing on the glass, then your plants are not responding. If everything is healthy, you have it all balanced, but if slime starts growing, you'll need to shorten the duration. Test your water once a week. If the algae appear, that's on you; otherwise, it's all good. Your LEDs seem to be functioning properly.
Read the full article: Comprehensive Fish Tank Algae Control Guide
