How to Prevent Algae in Hydroponics?

how to treat algae in hydroponics

Growing hydroponic plants can be an extremely rewarding experience. Everything from lettuce and strawberries to cannabis and more can be grown hydroponically. However, one issue that many people face when growing hydroponic plants and produce is algae. Algae infestations are unfortunately quite common, and there are multiple causes of them.

There are many different types of algae that may infest your hydroponic system, and today we want to take a quick look at each of them. This article will focus mainly on how to prevent algae in hydroponics, but will also cover why algae grows in the first place, what impacts it has on your hydroponic system, and more.

What Are Algae and Its Types in Hydroponic Plants?

Algae are living organisms, small photosynthetic organisms that live in moist or aquatic environments. Although many people think of algae as plant matter, this is technically incorrect.

As far as hydroponics is concerned, algae is able to flourish in any area that has sufficient water, nutrients, and light.

In nature, algae may be an indication of a healthy ecosystem, but for hydroponics purposes, algae are considered invasive nuisances that create a host of problems.


Brown algae is commonly found in colder northern waters, particularly along rocky coastlines. Many people refer to brown algae in the ocean as seaweed, and this type of algae belongs to the Phaeophyceae family.

It’s most often found in saltwater, but may also thrive in freshwater conditions. Brown algae is multicellular in structure, with those structures being filamentous. In hydroponics, brown algae can cause biofilm, which can then be home to harmful bacteria.


Black algae are single-celled organisms that are often found in hydroponics systems. Black algae are colony-based, and technically speaking they are a type of bacteria.

This type of algae often thrives in hydroponic systems that have unbalanced pH levels, poor filtration and bad water quality, and excessively warm water.

Although black algae itself generally isn’t harmful to your hydroponics system, it can cause clogs. It may also harbor a variety of other detrimental bacteria.


One of the most common types of algae found in freshwater systems such as home hydroponics setups is green algae. There are several types of green algae, including Chlorophyta, Mesostigmatophyceae, Streptohyta, Spirotaenia, Charphytal, and Spirotaenia.

Depending on the type, these types of algae can be multicellular, unicellular, or colonial. This type of algae is generally found in waters that are rich in nutrients and with great amounts of light.

Green algae may clog up your hydroponics systems, they create slippery films, and they tend to compete with plants for light and nutrients. In other words, they may outcompete your plants and end up killing them.


Although not as common as some of the others on the list, red algae can still be a problem in hydroponics systems. Red algae are generally of the Rhodophyta division. Although usually found in saltwater environments, this type of algae can also thrive in freshwater systems.

This is a mostly multicellular type of algae that prefers water that is rich in nutrients and has lots of light. In hydroponics systems, red algae can cause clogs and cause plants to compete for light and nutrients.

Bluish Green

Finally, we have bluish-green algae, which is green algae combined with the presence of cyanobacteria, therefore giving it that classic bluish appearance.

This type of algae thrives in water that is rich in nutrients and exposed to plenty of sunlight. This is one of the most harmful types of algae to have in the hydroponics system, as it can produce a variety of toxins that are harmful to plants.

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How Does Algae Growth Start in Hydroponic Plants?

Understanding all of the factors that combine to allow for algae growth is important to know how to prevent it in the first place.

It Starts with Algae Spores

Algae growth starts in hydroponics systems when algae spores are introduced into the system. Algae spores may be airborne and introduced through the air, contaminated equipment, or water. Algae spores may also come from the water that you are feeding directly into your hydroponics system.

Algae Reproduction

Given the right conditions, algae reproduce very quickly through both asexual and sexual means, with many types of algae also producing spores that are able to withstand extremely harsh conditions. This allows dormant algae spores to multiply and grow once they reach suitable conditions, such as a hydroponics system.

Algae Growth Conditions

Algae also requires a variety of conditions to be met in order to grow properly. For instance, algae require a lot of light, as algae are photosynthetic organisms. They need light in order to produce energy and to grow. The artificial lighting that comes from hydroponics systems is rather perfect for algae to thrive.

Algae also thrives in waters that are rich in nutrients, especially the big three NPK nutrients that you are using in your hydroponics systems. Along with nitrogen, phosphorus, and potassium, algae also thrive in the presence of various micronutrients. The higher the concentration of nutrients, particularly phosphates and nitrates, the faster algae will grow and multiply.

Next, algae do of course require water, something that is always present in a hydroponic system. Water reservoirs or areas that feature poor circulation create stagnant zones where algae are able to grow. Algae also requires a temperature between 68 and 86°F, or between 20 and 30°C, and these are temperatures that are common in hydroponics systems.

Prevention of Algae in Hydroponic Plants

To prevent algae from flourishing in your hydroponics systems, there are a number of methods at your disposal, and they should be used in combination.

Using Opaque Materials and Managing Light

Algae thrives when exposed to sunlight, which means that covering any exposed areas in your hydroponic system with opaque materials is recommended. Cover tubing, reservoirs, and other exposed parts where water and light may meet. Stopping the algae from getting light means stopping it from performing photosynthesis, effectively preventing it from multiplying.

Using Chemical Treatments

It is also possible to use chemical treatments in hydroponics systems to kill algae and to prevent it from occurring in the first place. Use 3% hydrogen peroxide at roughly 3 milliliters per gallon of hydroponic water, although excessive doses can harm plants. You may also use 0.25 parts per million of copper sulfate, as this is a known algaecide.

Utilizing Biological Control

Biological control is another option, as there are many products out there that can introduce beneficial bacteria into a hydroponics system. Some beneficial bacteria are designed specifically to outcompete algae, and therefore to prevent it from occurring.

Algal Predators

If you are looking to create a comprehensive setup, and engaging in a process known as aquaponics is something that you might be interested in, adding some fish into the equation is an option. There are plenty of aquatic species, such as fish and invertebrates, which feed on algae and can effectively control it.

Managing Environmental Conditions

Making sure to keep temperatures below 77°F or 25° Celsius is a good way to prevent or at least reduce algae growth. Make sure to maintain proper pH levels as well, while keeping in mind that algae generally prefer conditions to be somewhat alkaline. Therefore, keeping your hydroponics system slightly acidic may be enough to prevent this issue.

Filtration and Cleaning

Both your mechanical and biological filters can play important roles in preventing algae growth. These filters use physical filtration methods and beneficial bacteria to reduce algae growth. The regular cleaning of your hydroponic system, or in other words, manually removing algae, is another option.

Alternate Options to Prevent Algae

If the above options are not suitable for your hydroponics systems, there are some alternate options to prevent algae as well.

Barley Straw Rafts

A barley straw raft can be effective at combating algae growth in larger hydroponic systems. The aerobic decomposition that occurs when barley straw breaks down releases chemicals into the water that prevent algae from growing. It’s a very slow process and it’s not ideal for small time operations, but if you have a larger system, then it might be perfect for you.

Grapefruit Seed Extract

Interestingly enough, grapefruit seed extract contains a variety of compounds that are antifungal, antibacterial, and anti-parasitical. It’s also proven to be an effective method at killing algae in hydroponic systems without causing any toxicity to plants. Use around 5 to 10 drops of grapefruit extract per every gallon of water in your reservoir.

UVC Light

The other option at your disposal is to use UVC light. This is a special type of light used in aquariums, aquaponics, and hydroponics, designed to kill a variety of microorganisms, which includes algae. These lights can be very costly, but also quite effective.

Growers must use only certified products for this purpose and purchase them from certified stores or companies. Additionally, it is crucial to follow all safety measures, as UVC light can cause serious damage to the eyes.

How to Prevent Algae in Hydroponics

Impacts of Algae on Hydroponics

There are two main impacts that algae may have on aquaponics, and neither of them are ideal.

Oxygen Depletion

The main impact of algae in hydroponics is oxygen depletion. During the nighttime, algae engage in a process known as respiration, which is when it consumes oxygen and produces carbon dioxide.

The more algae there is, the more oxygen it uses and the more carbon dioxide it produces. Furthermore, algae also die, which consumes oxygen through the decomposition process.

This can be extremely harmful to hydroponics systems. If plants don’t get enough oxygen, they can start to develop root stress and root rot, which can damage or kill plants. At the very least, oxygen depletion will lead to your hydroponic plants having stunted growth and much lower yields.

pH Oscillation

The other negative impact of algae on hydroponics is known as pH oscillation. When algae performs photosynthesis it decreases the level of carbonic acid in the water, which causes pH to rise. 

Then, during the night time, algae releases carbon dioxide into the water, which then increases carbonic acid levels, which then causes the PH to drop and the water to become more acidic. The decomposition of algae can also cause pH levels to fluctuate.

This rapid and consistent pH fluctuation can be harmful to hydroponics systems, because PH swings may cause nutrient lockout. There are also certain elements that can become toxic to plants when the pH is not within its ideal range. Overall, this pH imbalance can cause great stress to plants, inhibit their growth, and end up killing them.

Using Oxygenated Water for Preventing Algae in Hydroponics

Adding oxygenated water, specifically hydrogen peroxide (H₂O₂), to your hydroponic system can effectively prevent and control algae growth it is commonly used among new and expert growers.

Most growers will recommend adding a 3% hydrogen peroxide solution, diluted at a rate of 1 teaspoon per gallon of water, which releases oxygen and kills algae without harming your plants. 

Adding Oxygenated water not only helps in controlling algae but also oxygenates the water, promoting healthier root systems and overall plant growth. Use with caution, as overuse can damage plant roots and beneficial microorganisms. This simple yet effective method ensures a cleaner and more efficient hydroponic system.

Prevent Algae in Hydroponics

Real-Life Use Case: Adding Oxygenated Water for Preventing Algae in Hydroponics

In an Ebb and Flow hydroponic setup, researchers tested how different amounts and frequencies of hydrogen peroxide application affected algae control and plant growth. 

They used two products, Zerotol and PERpose Plus, on peppers and tomatoes. Treatments involved applying 35 mL or 70 mL of hydrogen peroxide weekly and biweekly, along with a control group that received no hydrogen peroxide.

The results showed that higher doses and more frequent applications effectively reduced algae growth. Specifically, weekly applications of 70 mL of either product significantly decreased algae and improved plant growth metrics, including plant height, flower number, and both fresh and dry weights of shoots and roots. This demonstrates that using oxygenated water in the form of hydrogen peroxide can effectively manage algae while enhancing plant health in hydroponic systems.

According to the research, by applying 70 mL of hydrogen peroxide weekly, you can maintain a cleaner hydroponic system and promote better growth in plants like peppers and tomatoes.

How to Reduce Algae?

We’ve already covered virtually all of the ways to prevent and reduce algae in your hydroponics system, but let’s just summarize to make sure that you don’t suffer from this issue.

  • Using natural predators such as fish and invertebrates that feed on algae is a great way to reduce algae levels while also creating a beautiful aquaponics environment.
  • Using biological means, such as beneficial bacteria that will outcompete algae for oxygen and nutrients may also be a solution.
  • The regular cleaning of all necessary components in your hydroponics system, including the filter, will remove algae from the hydroponics setup.
  • To reduce algae, consider improving your filtration capacities and capabilities. A good three in one mechanical, biological, and chemical filtration unit should help prevent algae from occurring.
  • A UV sterilizer light should kill a variety of microorganisms, including algae.
  • Do everything you can to prevent light from getting into the water reservoir, as algae feeds on light and nutrients.
  • Make sure to maintain proper temperature and lighting conditions, as well as pH levels.

How To Clean Algae from Your Hydroponic System?

Cleaning algae from your hydroponic system is not overly difficult, but it does require a few key materials and a bit of diligence.

  1. Gather all necessary materials, including a cleaning solution of roughly 1.3 ounces of bleach for each gallon of water, some sponges and soft brushes, non-abrasive scrubbing pads, buckets, microfiber clothes, water hose, safety goggles, and gloves.
  2. Turn the hydroponics system off and disconnect it from any electrical sources to ensure that you are safe.
  3. You can now remove all of the plants from the hydroponic system and put them in an ideal location.
  4. Drain all of the nutrient solution from the channels and reservoirs. You can then disassemble all of the components that can come apart, such as grow trays, pumps, reservoirs, and tubing.
  5. Use a pressure washer or a water hose to rinse off any debris and loose algae from the components. This should get most of the algae, and whatever is left, you can scrub off using a scrub pad or soft brush.
  6. You can now apply the cleaning solution to all of the components. Submerge the components in the cleaning solution, and for larger pieces, use a cloth or sponge to apply the solution to the surfaces. Make sure to use scrub pads or brushes to scrub everything thoroughly and to make sure to kill all algae spores.
  7. You now need to rinse all of the components very thoroughly with clean water. You cannot leave any bleach on the components, or else it will harm the plants in your hydroponics system.
  8. Once everything is rinsed off and dried, you can then reassemble your hydroponics system.


As you can see, there are many different types of algae, and they can easily infest any hydroponics system. The trick to preventing an algae outbreak is to keep a clean setup and to maintain ideal conditions.


Algae can be harmful to your hydroponic plants because it can outcompete them for oxygen and nutrients.

Given the right conditions, it might only take a few days for algae to develop in a hydroponics system.

Black, brown, green, and blue-green algae are all common in hydroponic systems.

Chemical algicides are an option, although you need to be careful to not harm the balance in your hydroponics system.

If you see green or discolored slimy coatings on various surfaces, a musty smell, or cloudy water, then you might have algae.

To prevent algae from spreading, make sure equipment is clean, maintain adequate filtration, regulate nutrient levels, use opaque materials, and use a variety of preventative methods.

Hydroponics systems should be inspected at least once per month for signs of algae.

Yes, green algae can be harmful to hydroponic plants as it can compete with them for oxygen, nutrients, and light.

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