Water Storage & Rain Harvesting

How & Why Does Algae Grow in a Water Storage Tank?

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[fa icon="calendar"] Sep 2, 2020 9:30:00 AM / by Jim Arnot


One common problem that you may run into when storing your rainwater in a water storage tank is the presence of algae. By understanding the science behind how algae grows, you can be effective in eliminating algae growth in your water tanks. In this post we'll uncover the process in which algae grows.

How Does Algae Grow?

Algae are one-celled or multicellular organisms that contain chlorophyll. They grow through a process called photosynthesis. During photosynthesis, chlorophyll absorbs the light energy of all colors but green. The green light is reflected back off of the algae which result in its green color. The photosynthesis process is the means in which algae make food and oxygen for survival. It is an endothermic chemical process that uses sunlight to turn carbon dioxide into sugars. In order for photosynthesis to occur, a combination of carbon dioxide, water, and light energy must be present. When these elements are present, algae grow.

Simply put; Algae needs light to grow.

Factors That Affect the Growth of Algae

Many times, the growth of algae is not triggered by a single factor, but rather, variations of combined environmental factors. The following are conditions that will create and sustain the growth of algae.

  • Light: Algae needs light energy to grow. The more sunlight that penetrates the area, the higher the chance for algae to sustain life.
  • Nutrients: Nutrients, like nitrogen and phosphorus, fuel algae growth.
  • Temperature: Warmer water leads to increased algae growth.
  • Turbidity (water clarity)Particles suspended in water affect how light travels. The clearer the water, the more sunlight will penetrate.
  • Stable Conditions: Most algae prefer stable water conditions with minimal turbulence. 

6 Tips to Mitigate Algae Growth

If you are already harvesting rainwater or just getting started with the concept, there are a couple of tips that you should take into consideration to prevent the growth of algae.

  1. If you're starting fresh, the most effective way to prevent algae growth in your storage tank is to purchase a tank with LIGHT-BLOCK™ technology. Simply put; this stops light penetration through the tank sidewalls. Without sunlight, algae can't grow!


  2. If your tank does not have Light Block™ technology, put your tank in the shade, out of the sun.
  3. Paint your tank black.
  4. If your tank currently has algae growing in it, add 1/4 teaspoon of bleach to every gallon of water you store. Bleach kills microorganisms such as algae. The chemical behind this effective form of removing algae is known as hypochlorous acid. Once the bleach is added to the water, this chemical goes to work killing microbes and removes algae.
  5. Or, add 4 parts of chlorine to every 1,000,000 parts water. Using this small ratio, your water will be safe to drink or irrigate with. 
  6. Or, Clean the tank interior with mild dish soap and hot water one to three times a year.

Note: When using bleach or chlorine, it is important to follow the ratios of bleach and chlorine very closely to ensure that your rainwater is safe for irrigation as well as being drinkable!

Related Content: This Water Tank Eliminates Algae Growth

If you are getting ready to purchase a water storage tank, not all tanks are the same, especially when it comes to preventing algae growth. To prevent algae growth, investing in a water storage tank that features a total block out of sunlight is imperative (as demonstrated in the video above). This will prevent you from having to drain your water, scrubbing your tank, and waiting for rainwater to fill your tank again if you are harvesting.

I hope this info about how algae grows, has helped you. If you would like more info about water storage and rain harvesting, feel free to subscribe to our newsletter. If you are interested in premium algae resistant water tanks, you can check them out here.


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Jim Arnot

Written by Jim Arnot

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