How to Prevent Algae When Growing Cannabis?

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Added 23 April 2022

What organism is capable of photosynthesis, is mostly green in color, but not a plant?

The answer is algae.

Algae love moist areas, warm temperatures, and light — an environment resembling your cannabis grow room. 

Algae is very important to our ecosystem since they serve as a source of food for aquatic animals like fish, tadpoles, etc. Without them, we will perish. 

However, algae aren't suitable for cannabis plants, especially when you're growing indoors. They can create many problems from fluctuating the growing medium's pH, inviting pests and pathogens, and even suffocating the roots.

If you spot some algae growing in the grow tent, it's alright. However, since they spread very quickly, you need to take some steps. 

If your plant looks tired or has wilted or yellow leaves, with slimy-green-something growing on the growing medium, it is due to algae. You must fix this issue before it worsens, as it can damage your plant beyond recovery and reduce yields.

What is Algae?

As mentioned above, algae live on three things: moisture, light, and nutrients — just like your hydroponic system. However, they not only grow on hydroponic systems but also thrive well on soil- or coco-based grow systems. And in denser grow mediums, they can only grow on the surface.

Your system will be more susceptible to algae if you use living water (water with beneficial bacteria) or organic nutrient supplements, especially the NPK ones.

Algae is almost impossible to prevent, but you must try your best to control its spread. As mentioned above, it cannot harm the plant much in small batches. But, it can reproduce quickly, eventually creating many problems for your plant.

Where Does Algae Come From?

Microscopic algae

Algae has been around for 1.7 billion years, and over time, it has adapted to grow in various conditions. So, its cells and spores can be found everywhere around you. But for most cannabis growers, there are a few major sources that you must also be aware of.

The most significant source of algae in cannabis is water, especially if it comes from a shallow well or pond. Additionally, even public water lines often have an algae biofilm buildup on the interiors, which can travel into your nutrient solution reservoirs.

Another primary source of algae is the outdoor soil — it is rich in spores, which can get carried by the wind and blown into your grow room.

How Does Algae Grow?

Algae in reservoir

Algae are simple photosynthetic organisms. They use light to generate sugars and energy that help them survive, and unlike plants, they don't have leaves or roots for the same.

They make their way into your grow system in the form of microscopic spores, and once they land in a habitable environment, they quickly start developing cells and growing. So far, these small patches of algae are relatively harmless.

The problem arises when they multiply through mitosis, where the nucleus divides and produces daughter cells. This is when they start growing all over your growing system, which can cause several problems for your plant.

How Do They Affect the Plant's Health?

wilting cannabis

While algae do not directly attack the plant, their survival can cause several problems, such as the following.

They Suffocate the Plant by Oxygen Depletion

Algae's most significant damage to plants is oxygen depletion, and it does so in two ways.

First, it disrupts the roots' functions, impairing their ability to absorb oxygen and nutrients. Since algae thrive on the water surface, they form large clusters around the root systems, using roots as a supporting structure. 

Second, they steal oxygen from the roots. Algae are similar to plants — they inhale carbon dioxide and exhale oxygen during the day and vice versa at night. So, when the lights are turned off, they absorb oxygen, leaving the roots without it.

Plus, the CO2 they exhale during the night forms carbonic acid in the water, significantly affecting the root zone's pH levels. And the pH fluctuates every time algae switches from one gas to another.

They Can Clog the Pipes, Filters, and Pumps

Once algae have taken over the roots, they start growing into other areas of the hydroponic system, including the drains, water reservoirs, pumps, etc. If not taken care of immediately, they can start multiplying even more and clog the system's plumbing components.

This can wreak havoc on your nutrition cycle as it can either flood the systems or prevent the nutrient solution from reaching the plant in adequate quantities.

They Can Disrupt the Watering Routine

Similarly, they can even stop the water from reaching the roots. If algae grow on the medium's surface, they initially form a green blanket, which grows thicker over the following days.

After a few days, the green blanket turns black, dries up, and forms an impermeable crust on the surface, which can stop water from reaching the roots.

Plus, the green blanket of algae mimics wet soil, which may make you delay the watering cycle to let the growing medium dry. This can lead to a shortage of water for the plant.

They Invite Pests and Pathogens

Lastly, algae are notorious for inviting other troubles like pests and pathogens. 

Algae do not eat your plant — they don't have mouthparts — but they provide the ideal environment for other pests to thrive, like aphids, nematodes, fungus gnats, and midges. 

These pests feast on your plant's tender tissues, which can significantly damage your plant. Pests can hamper the plant's photosynthesis process, stunt growth, cause malnutrition, and many other issues. 

Additionally, algae can also invite other fungi to your plants, like pythium, septoria, and fusarium, which can cause various conditions like leaf spot disease and root rot.

How Do You Spot Algae on Your Plant?

algae in hydroponics

Algae are of various types, so the symptoms also vary wildly. However, the easiest way to spot algae on your setup is to use your eyes and nose.

Algae often grow on the reservoir's surface, growing medium, or on other surfaces in the form of green film, but they can sometimes be black, red, brown, or golden. Plus, they reek a lot — your plant will smell moldy or earthy.

These two symptoms are accompanied by other symptoms, which can help you spot algae growing underneath the surface. Here are the common symptoms.

  • Leaves wilt, turn yellow, droop, or grow slowly due to oxygen deprivation
  • The plant may experience stunted growth, wilting, or nutrient deficiencies due to pH fluctuations in the root zone
  • You may spot various pests and insects circling your plant or see signs of pest infestation like holes on the leaves
  • The roots may appear wilted, brown, or slimy due to root rot or fungus disease

How to Prevent Algae?

algae in water

It would be best if you always tried to prevent algae instead of eliminating it. So, if you want to prevent algae from forming on your precious setup, follow these tips.

Keep Everything Light-Tight

The most important factor algae require to grow is light, so you can prevent algae by depriving them of light. Even a minor light leak can cause algae to grow in your water reservoir.

So, ensure all the pipes, water reservoirs, and other areas where water passes through are entirely light-tight. Use thick black plastic that does not let light in, or you can even blackout the components with black spray paint.

Treat the Water

In some cities, the water supply has a lot of algae growing within it, which may end up on your plant. So, treat your water to remove algae from it altogether. You can use basic water filters or invest a little money in RO purifiers.

Remember — if you are using RO water, it will be devoid of any nutrients and minerals, especially calcium and magnesium. So add them back to the RO water using supplements to ensure your plant gets enough nutrients from the water.

On the same lines, ensure your watering cycle is apt for your plant. Avoid overwatering at all costs as algae grow best in moist and wet conditions. Instead, let the growing medium at the top dry thoroughly before watering again.

Keep Your Setup Clean

Whether you're using an aeroponic or hydroponic system, always keep it clean. Remove any decaying leaves or roots from the setup as they release nitrogen when they decompose, and algae love nitrogen. 

Also, it is recommended to flush the entire system regularly. You can use copper ionization, chlorine dioxide, and hydrogen dioxide to sanitize the components and prevent algae.

You must also keep the water fresh in the reservoir. So, change the water every ten days, and once the plant matures, you can change the water every week. 

Maintain the Right Airflow and Temperature

Lastly, keep your grow room's temperature in check. Algae tend to multiply much faster in warm environments, so maintain a temperature of around 21°C to 23°C to prevent algae from multiplying. 

And ensure your ventilation and exhaust systems work efficiently to keep the air in the grow room fresh. You can even invest in an air filter to filter out any algae spores coming in from the outside.

How to Get Rid of Algae?

Wondering how to get rid of algae from hydroponics systems? Well, you may not always successfully prevent algae. However, you need to be prepared to eradicate them from your grow room. First, use the above-mentioned techniques to stop the growth of algae.

Then, follow these techniques to eliminate existing algae from your grow room.

Use Hydrogen Peroxide

Hydrogen peroxide is a volatile compound that can destroy algae's cell walls, killing them instantly. And you can buy it at your local gardening store for a cheap price.

As a general rule of thumb, use only 3 ml of hydrogen peroxide per gallon of water and thoroughly clean all the algae-ridden surfaces of your setup. Still, follow the manufacturer's instructions for proper dosage guidelines.

Be careful though — hydrogen peroxide can burn the roots, so only use the recommended dosage.

Use Algicides

If you don't want to use hydrogen peroxide on your plant, you can even use other organic alternatives like baking soda or grape seed extract to remove algae.

If you use baking soda, mix 15 to 20 grams of it into your nutrient solution and feed it to your plant. As for grape seed extract, mix a few drops into a liter of water and scrub the surfaces with it.

Add Barley Mats

Lastly, you can even add barley mats to your water reservoir. These barley straws create a mat on the water's surface, preventing algae from growing within. Plus, they promote the growth of beneficial bacteria, which is always welcome.

Summary: How to Prevent Algae When Growing Cannabis?

Algae is one of the common problems almost all cannabis growers face at least once in their growing career, but it is only a minor convenience if you know how to deal with it — even better if you avoid algae entirely. 

Follow the tips listed above to prevent algae in your cannabis growing system. If you spot algae, sterilize and clean your entire system and restart again to prevent algae as much as possible, 



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