How Long Can Algae Live Without Light?

Algae are microorganisms that grow on aquarium walls, decorations, plants, and other surfaces or float freely in the water. All fish tanks will eventually develop some algae, which simply diverts attention from the tank’s aesthetic value. But excessive proliferation can be detrimental to the fish. Algae removal is an ongoing activity that is essential to maintaining a vibrant aquarium.

Algae need light to flourish, and lamps placed above fish tanks often provide that light. Keep the amount of light that your fish tank receives each day between six and eight hours at the most. Also, avoid putting it in a spot where it will be exposed to direct sunlight. This will reduce the amount of favorable environmental conditions that algae need to multiply.

This article explores the significance of light for algae to thrive in a fish tank and the precautions you should take to eliminate its rapid growth.

Why Do Algae Need Sunlight?

The only things that algae require to thrive are sunshine (or another form of sugar), water, carbon dioxide, and a few inorganic nutrients, including nitrogen and phosphorus. In addition, algae reproduce incredibly fast.

Algae, like other plants, produce food through a process called photosynthesis. This is the mechanism wherein carbon dioxide and water are converted into glucose (sugar) and oxygen using sunlight.

Algae are often aquatic unicellular or multicellular creatures that are autotrophic (meaning that they are able to sustain themselves via their own metabolic processes) and eukaryotic (meaning that their cells have nuclei and other specialized organelles). They require sunlight or any other source of light for their survival. There is no such thing as algae appearing out of nowhere by themselves.

The most likely reason why there seems to be a link between the amount of sunlight and the size of algae is that photosynthetic algae can get more energy when there is a lot of it, so they can grow and reproduce faster when there is a lot of light. In fact, this kind of growth can sometimes lead to blooms of algae.

The green pigment called chlorophyll absorbs photons, releases electrons, and synthesizes ATP and NADPH through chemical processes and proton gradients. NADPH powers the Calvin cycle, whereas ATP powers algae’s metabolic functions, such as converting CO2 into food like sugar. Algae use solar energy to convert CO2 into food and other chemicals.

So without sunshine, algae cannot photosynthesize and feed themselves.

Will Algae Grow Without Sunlight?

Even though algae lack roots, stalks, and leaves, they utilize photosynthesis for their own sustenance, making sunlight an essential component of the process. There are several varieties of algae. Although some algae like shade better than sunlight, the most common ones cannot grow without sunlight.

There are tens of thousands of species of algae and all fall into two types of algae, each of which needs either direct or indirect sunlight. Algae in swimming pools, especially the common green kind, thrive when exposed to sunshine. However, mustard algae thrive best under dappled light.

The presence of chloroplasts in algal biomass facilitates photosynthesis. Chlorophyll is the green pigment found in chloroplasts, which are organelles found in plants. This pigment plays an important role in the conversion process by soaking up sunlight.

Will Algae Grow with Indirect Sunlight?

Keep in mind that light, whether direct or indirect, is the accelerator of growth for both plants and algae. Sunlight increases the plant’s metabolic rate, thus protecting it is important. If the plant does not receive enough direct or indirect sunlight, it will be unable to meet its increased metabolic demands and may suffer as a result.

Because of this decline in health, the plant is less able to defend itself. The weak defenses are what allow the algae to take root. On the contrary, algae don’t need too much light to bloom and can rapidly proliferate even in indirect sunlight.

The absence of sunlight, direct or indirect, will make its survival impossible. Without photosynthesis, algae cannot feed or control their temperature. But if there is even the slightest amount of indirect sunlight, algae can grow and thrive. Moreover, there are several varieties of algae that grow in indirect sunlight or artificial lighting.

Can Algae Grow Under Artificial Light?

The effect of artificial light is widely debated as the primary cause of aquarium algae growth. Some attribute artificial light to algal proliferation, but others strongly disagree. However, if you’re using artificial or natural light for photosynthesis in your plants, the algae will benefit as well.

Under the effect of artificial light, many varieties of algae may develop. As matter of fact, many different kinds of algae are able to develop far more rapidly in the presence of artificial light than they would in the presence of natural sunshine.

It is certain that algae will flourish under artificial illumination if it has sufficient wavelengths for the photosynthesis process. Although algal growth may be stimulated by artificial illumination, not as much as by natural sunshine.

Certain aquarium lighting products are particularly designed to provide your fish with the light they require while preventing algae growth. Nevertheless, not all forms of artificial light are conducive to the growth of algae. For algae cultivation, the best forms of light to use are fluorescence, red LED, and white LED.

How Light Deprivation Prevents and Eliminates Algae?

If you deprive algae of light, you will either stop the growth of algae or completely eradicate it. This is because algae, like other plants, grow best in bright sunlight. The first thing to do is to cover the tank or aquarium so that it cannot get any light for several days. Ideally, a minimum of 4 days and a maximum of 7 days.

Depriving the availability of light is the primary factor limiting algal development, followed by nitrogen and phosphorus. Although carbon, silica, and other micronutrients are commonly overlooked, they are necessary for algal production, much like nitrogen and phosphorus.

Algae won’t perish right away if they aren’t exposed to light, but their expansion will be stunted. By removing the algae’s source of light, the growth of the algae is immediately halted. Consider using a treatment that reduces or eliminates the amount of light reaching the aquarium tank in order to prevent the growth of algae.

If you keep a close eye on how the algae respond to this approach, you won’t be able to tell much of a change until a day or two has passed. The most striking difference that will take place in your aquarium is that the algae will no longer grow at the same rapid rate as it did in the past.

Like plants, most types of algae thrive by photosynthesis. This process cannot occur if one of the key components, such as light, is removed. Without light, growth cannot happen.

Things You Should Know Before You Begin Light Deprivation?

Light deprivation is a tried and tested technique to eliminate algae. But this solution can be more effective if you consider certain changes in the light condition surrounding your aquarium.

  1. Unless you fully shut your fish tank off from the sun and the rest of the home, it will receive light even when the lights are off.
  2. Algae may be prevented by controlling aquarium light time. A proper light cycle benefits all tank species because fish and aquatic plants don’t require light 24/7.
  3. Instead of turning off the lights to eliminate algae, cover the tank with a light-proof material. This will better restrict algae-growing light.
  4. To prevent algae formation, keep your aquarium away from windows. Even if you turn off all the lights in the room, the sun can supply algae with adequate light.
  5. Aquarists typically offer too much light but not enough CO2 concentration or fertilizers. This causes plant growth issues, “melting,” and algae outbreaks. Measure CO2 levels with a drop checker when the lights are on and off. This will indicate whether to raise or reduce the CO2 dose.
  6. During the initial setup of your fish tank, 30-50% of weekly water changes will effectively fight algae. This reduces organic waste, primarily ammonia, as your tank matures.
  7. The flow rate from your filters and powerhead should be about 10 times the volume of your aquarium to keep things moving. So, for a 100-liter aquarium, the flow rate should be 1,000 liters per hour.
  8. Surface movement oxygenates the aquarium and prevents algae. However, excessive surface agitation promotes gassing off injected CO2. When the lights are off, use an air pump. Oxygen gas diffusion should last 6 hours overnight.


When a plant is healthy, its defensive systems can efficiently prevent algae from colonizing it. It’s important to keep an eye on your plant’s health if you notice any signs of excessive algae development, as this indicates a weak spot that is being exploited by the algae. Make light the only limiting factor in your aquascape, and you’ll be able to manage the plant’s metabolic needs, cut back on their resource use, and eventually wipe out the algae.


ALGAE: A naturally occurring phenomenon (

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