Getting Rid of Algae in the Grow Room

By Lacey Macri
Published: June 5, 2017 | Last updated: June 13, 2022 11:16:33
Key Takeaways

Here at Maximum Yield, we’re all about going green… unless that green happens to be algae in your growroom! Here’s a look at how these plant-like organisms can affect your hydro system, and how to kill—or full-on avoid—them.

Inevitably, algae will find their way into most every grow space on the planet.


It makes sense when you think about it. Although they aren’t classified as plants, algae are comparable photosynthetic organisms that grow in the same environment as plants. Specifically, algae thrive in an environment that is rich with light, warm temperatures, and nutrients.

In a hydroponic system, algae will grow and survive in water reservoirs, on the surface of grow media, and pretty much any other surface where the necessary resources are accessible.


Certain grow methods are more likely to promote the development of algae, including ebb and flow hydroponics, in which flood tables are often fully exposed to light and intermittently exposed to nutrient-rich solution.

Still, algae are very resilient organisms, and do not necessarily need ideal conditions to survive and even flourish.

In benign cases, algae don’t pose much of a threat to plants, despite the unsightly appearance and mildly unpleasant odor. However, if conditions are right, algae can reproduce rapidly, which creates other issues.


The first of these is pH fluctuations. In a similar way to plants, algae use carbon dioxide, nutrient, and light to produce oxygen through photosynthesis during light hours. At the end of the light cycle, the pH is typically at its peak.

The reverse happens during nighttime hours, when the algae begins to consume the dissolved oxygen that was produced earlier in the day, releasing carbon dioxide into the water through respiration.


The reaction of this carbon dioxide with the water creates carbonic acid, which causes the pH to drop. Significant populations of algae facilitate severe pH fluctuations during the cycle between daylight and nighttime hours.

All sorts of more serious issues can arise from the mere physical presence of algae, and this is where the domino effect really comes into play. Algae can clog plumbing, trap organic matter, and serve as harboring sites for pathogens.

Additionally, pests such as fungus gnats are more likely to enter the grow space if there is an attractive source of food for them to feed on (that is, decomposing algae).

Another issue that presents when algae populations get out of control is the risk of your plants suffocating. If plant roots are exposed to light, such as on open top flood tables, algae will begin to grow on the root masses, effectively suffocating them. In severe cases, the algae will compete with the roots for nutrient and the plants will suffer as a result.

Algae are virtually unavoidable if you are running a live environment using beneficial bacteria and organic nutrients. Also, due to its resilience, controlling or avoiding algae can be difficult, especially if you want to avoid sacrificing the health and safety of your plants in the process.

However, algae can be controlled a lot more easily and effectively in a sterile environment.

The most effective way to prevent algae from forming is to eliminate its light source. Some growing methods are a lot more conducive to this practice than others; for example, those where the roots of the plants are hidden from the light source, like in most deep water culture systems.

Regardless of the type of system you are running, however, it is important to black out (that is, make lightproof) as much of the exposed surfaces as possible.

This includes water reservoirs, tables, and any other pipes or tubes inside the space that contact water, nutrient, and light. Your containers, in particular, should be made of thick, typically black-colored plastic to prevent any light from permeating.

Good ol' hydrogen peroxide (H2O2) is also a go-to for those who grow in a sterile environment. It can control algae simply by adding it directly to the nutrient solution every few days.

A 29 per cent solution strength (three milliliters per gallon) is typically considered the industry standard, but more or less may be needed depending on the severity. Be careful, though; too much H2O2 can burn plant roots.

It is also important to keep temperatures down inside your grow space, including the water temperature. Algae thrives in warm water, so it is recommended to keep the temperature in the low 70˚F range.

There are reportedly other fancy ways to control algae, including UV filters, ozone, and a few home remedies. Many of these techniques, however, have mixed reviews as far as their effectiveness and potential side effects.

It’s best to stick to the basics. The easiest, safest, and least expensive control method is always going to be to shade or eliminate the light source where algae may grow right from the start.


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Written by Lacey Macri

Profile Picture of Lacey Macri
Lacey Macri works as head of sales at CleanGrow, focusing her time on business development within the company. She received a bachelor’s degree in communications and psychology from the University of California, Davis, in 2011, where she worked at the California Aggie student newspaper on campus.

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