Does Blue Light Cause Algae Growth? (The Quick Answer)

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A few years ago, a friend of mine told me that blue light is healthy for aquarium fish, as it helps them transition from day to night.

However, I also had an algae problem at the time and wasn’t sure if adding blue light would make it even worse.

Fortunately, over the years I have gained a lot of knowledge and experience in this field. And to make it easier for you, I gathered all the information into one article.

Let’s dive right into it.

Does Blue Light Cause Algae Growth In Aquariums?

Blue light can contribute to algae growth, but it is not the sole factor, and the type of algae and other factors such as nutrients in the water also play a role.

Algae are a form of plant matter, which explains their dependence on light. But which color do they favor?

This answer depends on various factors. Consider the following:

1. Blue Light And Algae Growth

Does blue light cause algae? The answer is yes, but not as a sole factor.

Marcel Gerard Jozef Janssen (Wageningen University, Netherlands) wrote a paper analyzing the impact of light and dark cycles on biomass yield.^[1]

He described algae as photoautotrophic organisms that thrived in water with sufficient oxygen, carbon dioxide, and various organic compounds.

This contradicts the notion that leaving an aquarium in direct sunlight allows algae to bloom drastically. It takes a combination of factors to boost algae growth.

Plants are the same. You can’t make them grow by overwhelming the tank with natural or artificial light. The foliage requires a healthy dose of fertilizers.

Therefore, you can’t blame blue light alone for the algae in the tank. The blue light will only benefit the algae if you have sufficient nutrients in the water.

2. Blue vs. Red vs. White Light

The relationship between these three colors is confusing because experts occasionally provide seemingly contradictory information regarding their impact on algae.

Some of them will highlight blue as the most beneficial of the colors. Others will favor red. Which is it? Well, it depends on the circumstances.

A study in the Journal of Introductory Biology Investigations compared all three colors and found that algae grew fastest under white light, followed by blue and then red light.^[2]

However, R.M. Forster and M.J. Dring (European Journal of Phycology) reached a different conclusion, sort of.^[3]

They found that pulses of blue light enhanced the rate of photosynthesis in species of brown macroalgae but had no impact on green and red algae species.

It should be noted that the researchers in question performed these tests in marine environments.

If you doubt these results, another study in Advances in Continuous and Discrete Models found that red LED lights created a conducive environment for C. Vulgaris to grow.^[4] Chlorella Vulgaris is a green microalga.

This Photosynthesis Research paper provided further confirmation by pointing out that cyanobacteria (Blue-green algae) grew faster under orange and red light and slower under blue light.^[5]

In other words, the algae type will determine the response you observe. But if that is true, why do people prefer blue light to red light?

In A Renewable and Sustainable Energy Reviews paper, S.P. Singh and Priyanka Singh (School of Energy and Environmental Studies, Devi Ahilya University) placed blue light at the top of the hierarchy, followed by white, green, and then red light.^[6]

Why is this? Science Daily has the answer. Water absorbs red light.^[7]

Blue and green lights have more penetrative power. They go deeper than red light. This makes blue more beneficial than red.^[8]

3. Blue Light And Aquarium Fish

Blue light is beneficial to fish. First of all, it allows them to gradually transition between day and night time. In the wild, the sun doesn’t disappear instantaneously.

The change is slow. Switching the lights in the aquarium off at night can cause stress. Blue light makes the transition seamless.

Secondly, blue light can reduce stress in fish, including aggressive species like bettas. Young fish in some species will develop faster and healthier in the presence of this color.

It should be said that healthy fish are an excellent solution to algae overgrowth. Some species will happily eat algae.

For your convenience, here is a list of 32 species that may or may not eat the algae from your tank. This applies to both freshwater and saltwater tanks.

It is also worth mentioning that blue light is excellent for aquarium shrimp, which in themselves are an ideal solution for algae overgrowth.

**Bristlenose Catfish are among the best algae cleaners in fish tanks.**

Does The Lighting Source Matter?

Technically speaking, the light source doesn’t matter. That being said, blue LEDs are more attractive because you can dim them.

Light intensity is just as important as duration. LEDs give you more control over both options. You can program them to deactivate at a specific hour.

Fluorescent lamps are less efficient because they generate so much heat, and higher temperatures can encourage algae growth.^[9]

This is why some people associate fluorescent aquarium lights with algal blooms.

What Is The Optimal Blue Light Range?

The most important considerations for aquarium lights are the PAR and PUR.

PAR stands for ‘Photosynthetic Active Radiation, which tells you the volume of photons each square meter of a plant absorbs per second.

PUR means ‘Photosynthetic Usable Radiation.’ This is the PAR spectrum a plant will use for photosynthesis.

Experts encourage consumers to use the PUR. This is because some light sources have a high PAR but produce very little usable light for the plants.

On the other hand, some lamps have a lower PAR, but their usable light is so much higher.

That being said, aquarists tend to emphasize the PAR. They usually target the 40-50 PAR range.^[10] This range allows your plants to thrive.

Healthy plants will suffocate the algae by out-competing the organisms for the tank’s nutrients.

But you shouldn’t hesitate to adjust the light intensity if the algae population is growing at an unexpected pace.

Keep adjusting until you find a range that allows the plants to thrive without encouraging algae growth.

Keep in mind that light is just one aspect among many that promote algae growth. You can’t fight algae by simply adjusting the light intensity.

Try to maintain a regular day/night cycle. That means giving the tank 8-12 hours of light and an equal duration of darkness; don’t keep the blue light on all night.

Ideally, the blue light should be left on between 18:00 and 23:00, and no longer than that.

If you’re uncertain about the light’s intensity, use the visibility to make your decision. Make sure the tank has just enough light for you to see the fish.

Anything more is unnecessary and potentially dangerous. Anything less is also unappealing because there’s no point in raising fish if you can’t see them.

Fortunately, fish tanks are resilient. You can experiment for as long as you want until you find a satisfactory balance. And if things go wrong, empty the aquarium and start again.

**Blue light mimics moonlight, which is why many aquarists use it at night.**

What Color Light Stops Algae Growth?

No color light stops algae growth, not directly. Most colors will benefit the algae in your tank.

Green is your best bet if you’re looking for a color that doesn’t contribute to algae growth.

It cannot actively combat algae. However, it won’t boost the organism’s growth either.

This is because green photosynthetic organisms reflect green light instead of absorbing it. People use green lights to improve the appearance of their aquatic plants for this reason.

How Else Can I Control The Algae In My Tank?

As mentioned earlier, you can reduce the intensity of the lighting, and even the color, if you have plenty of algae in your tank. Fish can also help in this matter.

But there are a few more things you can do. Start with routine aquarium maintenance.

I have previously explained that nitrogen elements, including ammonia, nitrate, and nitrite, have a direct effect on algae, which feed on these toxins.

Therefore, if you control the amount of waste in your tank, you will reduce these toxins and prevent the algae from spreading.

Be sure to change 15 to 20 percent of the water each week. This will keep the ammonia levels at 0 ppm.

I also recommend vacuuming the substrate at least once a week. This part usually contains a lot of debris and fish waste that rots and produces toxins.

For this, I use the Laifoo Vacuum Cleaner (link to Amazon). This product is extremely affordable and incredibly effective.

Pro tip: Here is my complete guide to aquarium ammonia, where I’ve shared all the essential information about what causes it and how to get rid of it.

A great YouTube video discussing whether it’s a good idea to leave the blue lights on all night and how it affects algae.

Conclusions

Blue light can cause algae to grow in your fish tank, as well as red and white colors. However, this factor alone will not cause algae to grow.

If your tank does not have the nutrients required for algae, the blue light will have no effect. The most common nutrients are nitrogen compounds, such as ammonia and nitrate.

So, if you do routine water changes and vacuum the substrate on a regular basis, don’t be afraid to use blue lights. They are a great addition to fish tanks.