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How To Keep A Pond or Rainwater Cistern Clean of Algae – A Season Recap

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Rainwater cistern in Shawna Coronado's front lawn.
Shawna Coronado's rainwater cistern fountain in winter.

Several years ago I had an Aquascape RainXChange system – basically, a rainwater cistern with a fountain – installed in my front lawn (if you want to see how we did that, you can click the link or I have included the video at the bottom of this post). Water collects in the cistern off my roof, then I can choose to water my garden with the rainwater or simply enjoy the fountain which is on top of the cistern.

Now that I have had the system for several years, I can say it works marvelously. Several times per year I have to clean off string algae which forms on the fountain. Since I am concerned with keeping the system “good for the environment” and healthy, I do not want to use chlorine or some other dangerous chemical to clean the algae blooms. In the summer, I turn off the fountain during the night and let it dry out to help prevent algae blooms. In the winter I let it run all season and it forms some astounding ice formations, but develops no algae in the cold.

Usually I turn off the fountain, let it dry, then power wash the algae off at least three times a year. This season I tried something different. I experimented with products labeled environmentally safe pond/cistern cleaners. Two companies approached me about sampling their products and sent them out to me at no cost so I thought I would try both and report to you how it went. I did not power wash the fountain once this season, but instead tried to use the products regularly as a preventative method. Below are the end-of-season results.


SI Pond Cleaner

Cistern Cleaners

A. Bio S.I. Water Doctor – 

Bio S.I. Water Doctor for ponds is labeled non-pathogenic and non toxic and environmentally safe. Ingredients include bacteria and microbes which reduce the algae blooms. It does not work as quickly as other chemical treatments for algae blooms, however, after using it several times this summer, it has been effective and works quite well for our purposes while not harming the wildlife. I will continue to use this product. I use it once a month for maintenance.

B. GreenClean Granular Algaecide –

Green Clean pond cleaner

Cistern Cleaners

GreenClean is made by BioSafe Systems, which is known for it’s “A Green Brain is Better” campaign. It is very effective for killing algae. Online it says it is OMRI listed and has eco-friendly “chemistry”. However, after reading the label carefully I found out this product is corrosive in powder form and causes irreversible eye damage if the product is somehow splashed in the eye. Additionally, the label is titled “Green Clean”, but then says this is a pesticide and is TOXIC TO BIRDS. While the online information says it’s safe for birds, I feel the labeling is confusing and would prefer not to take a risk with my birds. I have birds that are regularly playing in my rainwater fountain and do not want to hurt them. I have decided not to use this product in the future because of the inconsistent labeling.

*Special note – – Aquascape, Inc. sponsored the installation of this residential RainXchange System in exchange for my services. BIO S.I. and Green Clean Granular Algaecide were given to me as samples to try out the products. These sponsorships do NOT effect my opinion about rain water collection or rain water cisterns, which I believe are amazingly good for the environment.

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  1. Love the Rain Water Capture System. I have several 45 gal drums to interconnect which should save a substantial amount of city water for water the garden. The proximity of your compost bin is an excellent idea. I need to move mine to where my water capture system will be. Maintaining moisture in the compost pile has been an issue. I would like to see a video on Compost ideas. I Think your Bin usage is far more productive than my Compost Pile. Thanks so much for your Earth Friendly videos. Your passion is inspiring!

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