Algae in My Homemade Hydroponic System

by Mark
(North Carolina)

I'm about 3 weeks in on the hydroponic setup you describe as your best homemade system, and I'm starting to see some algae build-up. Is some algae typical, or do I have a problem Houston?

Answer: Mark, algae by itself is not a terrible problem. The algae does compete for nutrients with the roots of your plants, which can slow down plant growth a tiny bit (hardly noticeable). However, algae dies and is decomposed by microscopic fungi. These microscopic fungi, in turn, attract fungus gnats. If fungus gnats successfully infest your roots, they will chew hundreds of tiny holes into your roots. Each of these holes is an open wound, inviting any pathogen that happens to be present in the nutrient solution to come and infect your plants.

Unfortunately, there are ALWAYS other pathogens present in the water. Therefore, the best strategy is to prevent any physical damage to the roots- and therefore prevent any other pathogens from gaining a foothold. This means preventing fungus gnats and minimizing the growth of any algae.

Algae will grow whenever these three things are present: water, nutrients, and light. In order to prevent algae growth, you need to eliminate any spots in your hydroponic system where the nutrient solution becomes exposed to light. Mostly, this means using a light-proof nutrient reservoir *with a lid*. Also, check the spots where nutrient solution enters the system and where the nutrient solution returns to the reservoir.

There are a couple of other things you can do. Keeping the nutrient solution between 65 and 68 degrees will cause the algae to grow more slowly. Also, keeping the nutrient solution well oxygenated helps eliminate pathogens in the solution and encourages healthy root growth. Finally, using small amounts of Hydrogen Peroxide in the reservoir will help eliminate pathogens, kill algae, and keep the nutrient solution oxygenated.

If you decide to use Peroxide, be sure to read my using hydrogen peroxide page. This page goes into much more detail about how to use Hydrogen Peroxide safely and effectively, and why you DO NOT want to use the 3% peroxide in a brown bottle that you normally find at your corner drugstore. I hope this helps you out Mark, and Happy Growing!