Controlling and Detecting Algae in Hydroponic Cannabis Grows

Controlling Algae
January 12, 2021

Algae are a fact of life for hydroponics marijuana growers. In small numbers, they do not pose a threat. Once they bloom and their population multiplies out of control, all sorts of things can happen – and they will not be good. In other words, you have to get rid of them as soon as possible to keep your plants safe.

Algae are small plants, a diverse group of microorganisms that conduct photosynthesis. Some are unicellular, while others are complex. They do not have a root system, stems, and leaves.

Green Algae are the most common, and most likely what you would see. Usually, it will have a slimy appearance. Yellow or Mustard Algae, likewise, are slimy and more challenging to remove. Black Algae, on the other hand, is a waterborne spore and the least common. Once it blooms, removing them can be nightmarish.

How Damaging are Algae to Marijuana Plants?

A small population of algae does not cause harm. They do have an unsightly appearance and terrible smell. Once the conditions are favorable, they can reproduce at a rapid rate – and that is when it becomes a problem.

Like other plants, algae use light, carbon dioxide, and some nutrients to photosynthesize and produce oxygen. At the end of a daylight cycle, the pH level usually remains stable. During the dark period, the algae consume dissolved oxygen produced during the daytime while releasing carbon dioxide into the water.

CO2 reacts with water to produce carbonic acid, which lowers the pH level. A large number of algae can cause a severe pH fluctuation between daytime and nighttime periods. Consequently, the plants suffer from failure to absorb some essential nutrients. They can also grow on root masses, causing suffocation. Always monitor and ensure you have correct pH levels to avoid nutrient deficiencies and other problems like algae.

Algae causes other problems, too. It can clog plumbing, trap organic matters, or serve as breeding grounds for pathogens. Moreover, it is an attractive food for pests such as fungus gnats.

How do you Get Rid of Algae?

You cannot stop algae. However, you can make it nearly impossible for them to grow by taking away one thing they need, apart from nutrients and water – light source.

Some hydroponics systems, by design, keep the roots hidden from a light source – such as deep water culture. Any system you use, the most important thing to do is to light proof exposed surfaces.

A reservoir made of translucent material would be helpful because you can quickly see what goes on inside. No one uses that, and you should not. Instead, you should use black to prevent light from penetrating through the bucket. Others that you should lightproof include pipes and any surfaces that have contact with water and nutrients.

Algae thrives in warm environments. One thing you can do is to keep the hydroponic nutrient solution at 70˚F range.

Once you notice algae growing, you can use hydrogen peroxide (H2O2) to sterilize the environment. The common practice is to add 3 milliliters H2O2 per gallon of water. Depending on the severity, you can add a bit more or reduce. Be mindful of adding too much as it can burn root systems.

A couple of other ways to help control algae bloom are:

  • Add UVC lights, such as those used in aquariums, in your filtration system to stop algae before they reach the grow space.
  • Adding 10 drops of grapefruit seed extract per cup of water is an organic way of getting rid of algae. You can mix it into the nutrient solution. Optionally, you can also spray full concentration directly on areas where algae appeared.
  • Barley straw mats are safe for the plants. Place them in the reservoir, and that would help eliminate algae.

What Other Ways Are There to Prevent Algae Bloom?

Water source contamination may increase the likelihood of an algae bloom. For example, using water taken from a lake or river, which may contain spores.

Most people use tap water. In some places, the water may contain other chemicals and minerals that can cause problems for the plants. Before using, it is best to draw the water and let it sit for 24 to 48 hours, allowing chlorine or other chemicals and minerals to settle or dissipate.

For hard water, even if you were to let it sit, it does not necessarily remove the suspended minerals. In this case, you might consider using a filtration system. Reverse osmosis, for example, makes the water pass through membranes to trap particles. An activated carbon filter is another option. These systems remove impurities in the water, which you can use with a hydroponics system.

For simplicity, buy distilled water, which is widely available, cheap, and saves you the hassle of having to draw water and sit for 24 hours.

One thing you should also do is change the water frequently. Some people do that every 10 days during the early growth stages, and every two weeks until the plants reach 12 inches in height. From then on, you should replace the water every week.

Apart from light proofing your hydroponics system, keeping the water clean and the environment sterile is the best you can do to keep algae away.

Algae Is Unavoidable But Easy to Control

An algae spore can travel immense distances. Sooner or later, one or more is bound to find its way into your hydroponics system. As long as you keep the grow room clean, surfaces sterile, and light proof anything that touches the water and nutrients, you can minimize their growth.

A simple home remedy using H2O2 is effective in removing algae, and so are other means such as grapefruit seed extract. If they ever become a problem, the fix is easy. Although you cannot avoid algae, they are not likely to become a significant problem as long as you follow the recommendations in this article.

If you’re having other problems relating to hydroponics, check out the Homegrown Cannabis Co. Forum Hydroponics section for further advice and troubleshooting.