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Algae – It’s Not Easy Being Green

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Kermit the Frog knows what it’s like to be misunderstood.

To conquer algae, one must think like algae.


Confusion over exactly where the assemblage of organisms commonly called algae fits in scientific classification has been debated for years and adjustments are continuous. The estimated number of species has varied, but the tally hovers around 20,000.

While green species of algae are most abundant in fresh water ponds, there are also red and brown types. The colors are determined by carotenoids in the chloroplasts of the organism. Some are tiny floaters, while others are filamentous strands attached to surfaces in the water.  (Note that the green stuff in the frog photo is probably duckweed – creative license applied.)

For simplicity’s sake, in this article, all the green, red, brown, stringy, slimy or spongy growth that crops up in ornamental ponds will be called Algae.

algaeWhat makes us hate them so?

Algae are photoautotrophic. That is, they take elements, such as nitrogen and phosphorous from water, mix them with sunlight and produce their own food. Through photosynthesis, they produce oxygen, just as terrestrial plants produce oxygen, making them important to the livelihood of humans and all creatures, great and small.

So far, they sound like welcomed inhabitants.  They produce oxygen while ridding the water of potential contaminating elements, like nitrogen produced by fish, for example.

Algae are nutrient rich and important to the diets of a huge array of other life on earth, including humans. Some are marketed as “superfoods”, such as Spirulina – another point towards salvaging their downtrodden reputation.

Tireless workers, they are sometimes used in sewage treatment, reducing the need for chemicals in the process. Algae has also been used in agriculture to capture fertilizer runoff from farms, with the added value of returning that nutrient rich algae into fertilizer that can go back into agriculture. That is a fine example of sustainable farming.

algaeOh yes, they can be productive members of our society, but if your pond begins to look like a sewer treatment project or an algae farm, then Algae has crossed the line and become a nuisance; thus the bad reputation. They do produce oxygen, but their rapid reproduction can quickly turn good Algae into scoundrels. When unemployed and congregating in gangs, they become ugly.

Balance is the key.

True for all ecosystems – balance is essential to the health of the system. Even oceans are susceptible to occasional nuisance levels of algae. Some algae will produce toxins that can be harmful to humans. Shellfish may accumulate dangerous toxins after filtering algae from water as food. Public service agencies monitor for such events, so they can post warnings. The main difference is that oceans are natural, open systems and will self correct. In a contained, artificial environment such as a fish or lily pond, the balance may need some intervention.


Prevention is the best medicine.

In essence, prevention means starve the algae. Here are some ways to make life difficult for them:

  1. As a general rule, allow 100 gallons of water for every 6 inch fish to control nitrogen from fish waste. Algae love nitrogen – yum yum. The most common element to tip the scale in water gardens is too many fish per volume of water in the pond.
  2. Keep leaves and other organic material out of the pond – manually and with the help of skimmers, vacuums and filtration systems (cleaned regularly). Supply some beneficial bacteria to help with this chore. They are natural maintenance workers, eating organic matter as a full time job. Organic matter also supplies food for algae. Once algae reproduce, they provide themselves with food – they consume their dead and it’s a vicious cycle!
  3. Dig the pond to a minimum depth of 24” to reduce sunlight infiltration. Algae depend on sunlight for photosynthesis and cannot live without it. They also thrive in warmer waters, so shallow water is their favorite – warm and sunny.
  4. Keep a variety of plants in the pond. They compete for nutrients and  block sunlight (especially water lilies), much to the dismay of sun-loving algae. Also,  Natural dyes can be added to the water reduce sunlight penetration.
  5. Add Barley Straw Extract or 1 Barley Straw Bundle per 1000 gallons of water. Barley straw naturally adds beneficial enzymes, lowers the pH and creates peroxide which can kill both filamentous and planktonic algae.
  6. Aerate, filter and circulate the water. Make sure the pump and filter system is large enough – bigger is better. This reduces warm pockets, accelerates filtration (clean filter regularly) and adds oxygen (decomposing debris depletes oxygen).
  7. Provide a place for beneficial bacteria to grow, such as a bio-filter, rocks, plants, filter media.

When prevention is not enough …

Fossils indicate that algae have inhabited earth for around 3 billion years, so prevention is not always going to do the trick. Algae bloom is a natural occurrence, common in spring, when the water warms, nutrients from over-winter debris is available, and competing plants lag behind. Methods to help re-gain balance are as follows:

  • Begin cleanup by manual removal of as much algae as possible. If any remains attached, scrub surfaces with a soft brush.
  • Clean filters at least once per day until under control.
  • For spot treatments, a good solution is Aquascape’s EcoBlast (you basically sprinkle it right on the algae)
  • Add aquatic plants – enough to cover 50%-70% of the water surface. Water lilies, Anacharis, and Water Hyacinth will shade the surface of the pond and compete for nutrients.
  • Add sludge eating bacteria at the recommended rate.

After the cleanup, being diligent about preventive maintenance comes naturally.

Photos, thanks to the following artists:

“Mt Misery_DSC_2545_8bit by SkyprPhotography, on Flickr

“Pond green with algea by thriol, on Flickr

“Pond and Bucket by Smabs Sputzer, on Flickr”

algae backyard pond barley straw Barley Straw Extract beneficial bacteria bio-filter bog plants carotenoids chloroplasts cleaing the pond ecosystem enzymes Featured Posts filamentous strands fresh water ponds Goldfish koi koi pond lack of oxygen lotus Organic matter photosynthesis planktonic algae pond fish Spirulina toxins water clarification Water Health water lilies Water lily water quality

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