How to Prevent & Fix Hydroponics Algae

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Hydroponics algae
Author avatar By Parker Curtis
March 17, 2022
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Nearly every hydroponics grower has to face the reality of hydroponics algae at some point. They all have a story to tell on what works best.

Helpful tips on how to get rid of algae in hydroponics setups will surely pique your interest if you’re growing this way. 

And our hydroponic algaecides pros and cons might just be what you’re looking for in the fight against algae in hydroponics. 

Whether you’re an old hand at hydroponics farming or a newbie, this to-the-point guide tells you how to prevent algae growth. Let’s begin.

Hydroponic cannabis plants
Hydroponic cannabis plants

What are hydroponics algae?

To understand the term hydroponics algae, you’ve got to look at its word stems.

The first word, hydroponics, has to do with hydro, or water. It’s a technique to grow plants in water instead of soil.

By dissolving some mineral solutions in the water, you’re able to grow nearly any plant using water only. The advantage of hydroponics is that it’s safe, sustainable, and easy on the pocket.

‘Ponics’ means to work. Working in water is what hydroponics comes down to.

Algae in hydroponics are less positive, though. Algae is a weed. It loves light, warm temperature, water, and nutrients. Exactly what your hydroponic weed plants also love. 

The problem is that algae can end up killing the plants that you want to grow, leaving you with a rather foul smell instead of big, juicy buds.

Hydroponics algae come in a variety of colors and textures, from slimy green and yellow to a stringy black nightmare that doesn’t want to wash off.

The really bad thing about hydroponics algae is that they sneak into your tanks or buckets unnoticed by microscopic air-born spores. Before you know it, your plants are dying, and there are algae everywhere. 

A real horror movie in your backyard!

Are algae bad or good for plants?

Hydroponic algae in small amounts are not bad for your plants. As a matter of fact, all hydroponic farmers know that it’s impossible to completely remove algae in hydroponics. 

Once your hydroponic tank’s glass turns green and is covered in hydroponic algae, it’s time to grab your sponges, buckets, and some chemicals.

Is algae bad for your plants, you ask?  Let’s take a look at why this extreme action is necessary.

Firstly, too many algae growing on the glass in your hydroponic tanks block the light you need for your plants to grow. No sunlight, no harvest. 

Secondly, it attracts all kinds of flies and fungi, which can eat or kill your plants. 

Thirdly, hydroponic algae absorb the oxygen in the water and air during the night, change it into carbon dioxide, and release carbonic acid into the water. This suffocates your plants. 

Algae do have one good quality, though. Once you’ve managed to kill it, it makes an excellent fertilizer for your garden.

Overall, algae in your hydroponics is a big baddy-o, and you need to limit its growth as much as possible.

Will algae affect plant growth?

Yes, hydroponics algae affect plant growth. Once it multiplies and covers the glass or bucket from your hydroponic farm, your plants won’t receive enough light to grow.

Hydroponic algae attach themselves to the roots of your plant. Your plant cannot absorb the dissolved nutrients that it needs. It’ll grow into a knotted bunch, unable to provide the plant with food, leading to death.

Cannabis pests and fungi love to feed on the algae. It might sound like a solution, but they don’t know the difference between algae and plants. They end up eating your crop as well.

Without enough oxygen, your plants can’t draw nutrients up through their roots and stems. Unless you do something quick, your plants will suffocate and die.

Apart from the devastating effects that hydroponics algae have on your plants, they can also clog the pipes, grow into the pumps, and damage your electrical equipment. This can result in some costly repair work for you.

The best way to ensure you can harvest hydroponic buds is to get rid of hydroponic algae as quickly and efficiently as possible.

Cannabis roots with algae
Cannabis roots with algae

How to prevent algae growth in hydroponics

You can’t prevent algae from growing in your hydroponics. As mentioned before, in small amounts, it can’t do much harm. The problem is that you need to prevent it from getting out of hand.

There are many ways on how to stop algae growing and how to get rid of algae in hydroponics once it becomes a pest. 

As they say, prevention is better than cure. So, let’s take a look at the best methods on how to prevent algae in hydroponics.

Algae preferenceActionResult
LightCover all exposed water, pipes, and pumps with opaque material
Use a dark-colored tarp for large hydroponics operations
Barley straw rafts also work
No light will penetrate, and algae can’t grow
Cut holes for the plants but cover the rest of the area
Barley straw rafts release chemicals as it decomposes, killing hydroponics algae
LightDeep water cultureLight cannot penetrate in deep water for algae to grow
Warm temperatureRegulate water temperature to stay around 70°FWater is warm enough for plants but not warm enough for algae to grow.

Another solution is grapefruit seed extracts. It’s an organic and eco-friendly option to prevent algae growth. Use 5–10 drops in a cup of water. Mix it into your nutrient solution or spray it directly onto the algae.

What color light stops algae growth?

If normal light or sunlight increases algae, then what color lights stop algae growth? Use green or red lights in your hydroponic tanks to reverse and slow down the growth of algae.

Installing UVC lights, the same you use for a fish tank, prevents the growth of hydroponics algae. These lights are quite costly, though.

Cannabis plant in a hydroponic system with covered water
Cannabis plant in a hydroponic system with covered water

How to stop algae from growing

Blocking light didn’t work so well? You might have a problem with algae already in your hydroponic system. The next step is to clean your system.

It’s important to clean your whole hydroponics system after every harvest to stop algae from growing. Algae spores can attach themselves to any surface: walls, light, and even you. 

Since they’re so small, you can’t detect them in time to stop algae from growing.

Directly after every harvest, follow these steps to clean your system before planting a new crop.

  1. Drain the water from the tanks or pond. Pump it out if you have the equipment, or let it drain away. 
  2. Remove all the electrical equipment and attachments.
  3. Dry the water or pond with cloth thoroughly once all the water has drained.
  4. Remove the pipes, disassemble the pumps and other equipment.
  5. Wipe everything clean, even if you don’t see any hydroponics algae growing on it. Use a bottle brush to clean the pipes.
  6. Next, make the following sterilizing solution:
    1. hydrogen peroxide: mix 3 milliliters per one gallon of water or
    2. unscented bleach: mix 1 unit per 100 units of water.
  7. Assemble all the parts of your hydroponic system.
  8. Fill the system with purified water—a little higher than usual.
  9. Add the sterilizing solution.
  10. Start the pumps and let them pump for 4–6 hours to get rid of algae in hydroponics.
  11. Wash all the walls, windows, and furniture near your setup.
  12. Drain the tank or pond. If you’ve used bleach, repeat this step 3 times.
  13. Once drained, wipe everything with clean, sterilized towels.
  14. Your hydroponic farm is ready for planting.

How to get rid of algae on cannabis plants

Knowing that algae in hydroponics bloom wildly, it’s no surprise that cannabis grown in water or greenhouses can experience an algae attack sooner or later. That’s why prevention is key.

As with any other plant, be vigilant to prevent hydroponics algae from flourishing.

Cannabis plants indicate an algae problem by showing the following symptoms:

Check the pH level of your water regularly to ensure enough nutrients are being absorbed. 

Clean the tanks often and replace them with fresh water. Try not to use water from the tap or nearby rivers or ponds. It could be infected with spores causing hydroponic algae. 

Use water that has been cleaned of impurities. The process of reverse osmosis, or filtering water through activated carbon filters, prevents algae growth. 

The easiest way is to buy distilled water. It’s available, cheap, and ready for immediate use.

Once you’ve planted your cannabis, change the water every ten days during vegetation. When your plants have established themselves and are growing well, change the water every two weeks.

When your cannabis plants reach 12 inches, change the water weekly to prevent algae growth.

After you’ve harvested your cannabis flowers, follow the steps outlined above to clean the whole system and prevent algae from growing. 

Hydroponic algaecides

Hydroponic algaecides seem to be a quick solution once you’ve got a problem with hydroponics algae, but it might turn out to not be the best choice over time. 

Hydroponic algaecides can cause a lot of damage to your plants. Prolonged usage of algaecides weakens your plants’ natural ability to protect themselves against pests—including algae.

As the plant becomes weaker, this stimulates the growth of algae, and in the blink of an eye, you‘re faced with an algae plague.

As you apply more hydroponic algaecides to prevent the algae from spreading, it weakens your plant more, resulting in a cycle that’s difficult to break.

Combining your hydroponics plant farming with fish farming? Then using hydroponic algaecides is a huge no-no. You’ll end up killing your fish instead of the algae.

Are you trying to get rid of hydroponics algae for good? Instead of using hydroponic algaecides, you can opt for more eco-friendly and organic options like grapefruit seed extract or barley straw rafts. 

Remember to remove the barley straw once it starts to dissolve together with the dead algae. Dead plant material uses the oxygen in the water, which can result in killing your plants. Not to mention the not-so-friendly odor that accompanies dead plant material.

Cannabis healthy roots in hydroponic system
Cannabis healthy roots in a hydroponic system

Goodbye to hydroponics algae

Algae in hydroponics can ruin any dreams of a good harvest. Check your plants regularly for any sign of hydroponics algae spreading rapidly.

The best solution is to prevent algae from growing by reducing the amount of light reaching the water. Covering the water with dark material, tarps, or barley straw rafts helps you get rid of hydroponic algae.

You’ll also need to cover all pipes, pumps, and electrical equipment.

Controlling the temperature of the water, and cleaning everything with a sanitizing solution after harvesting, is important to prevent the growth of algae in hydroponics. Now you’ve succeeded in getting rid of your algae problem, start your clean hydroponics cannabis farm with high-quality seeds procured from Homegrown Cannabis Co.


About the author: Parker Curtis

Parker Curtis has around a decade of cannabis-growing experience, specialising in soil-less and hydro grows. He’s mastering outdoor, greenhouse, and indoor grows.