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Algae in Freshwater Aquariums and Ponds: a Primer – Part 1

Hello, Frank Indiviglio here.  I must confess that I like algae, perhaps because many of the creatures that I favor – shrimp, tadpoles, snails, loaches and others, do best in algae-rich tanks.  I’ve even encouraged algae to grow on the backs of aquatic snakes and turtles in zoo exhibits, much to the chagrin of the higher-ups! 

But, of course, algae certainly can get in the way of enjoying one’s pond or aquarium, and may endanger the health of the animals living therein as well.

Algae Diversity

Algae, which are not true plants, exist in a bewildering number of species.  For our purposes, we can roughly classify the commonly-encountered varieties as follows:

Green algae (hair, beard algae) thrive in well-lit situations.

Brown algae do well in low light.

Blue-green algae (actually a type of Cyanobacteria) and red algae live mainly in marine environments.

Controlling Algae

Nitrates and phosphates are the primary nutrients utilized by the most types of algae…limiting their concentration is the key to effective and safe algae control.

Algaecides and other “quick fixes”, while effective in the short term, do not address the root of the problem.  I always recommend that aquarists take the time to identify the reasons that algae has become established.  I have found this to be the most effective approach to algae control, be it in a betta bowl or a 77,000 gallon zoo exhibit.  And, because we learn much along the way and often utilize a number of fascinating animals and plants, the process is also very rewarding.

I’ll first discuss control methods that can generally be described as “natural” and will then mention a few more intensive alternatives.

Bacteria

The most effective algae enemy we might employ comes, surprisingly, in the form of another one-celled “non-plant/non-animal” – bacteria.  Many species consume the same nutrients as do algae, and can out-breed and out-compete even the hardiest types.

A number of species of beneficial aerobic bacteria (those requiring oxygen, which are also vital to water quality) will colonize gravel, filter media and other surfaces bathed in aerated water.  They will build up incredibly dense populations over an under-gravel filter, rendering it very difficult for algae to get a foothold. 

Nutrafin Cycle, which contains living bacteria, is especially effective in introducing these organisms to aquariums.  A number of other supplements, effective in fresh water and marine aquariums, are also available.

True Plants

Aquatic plants are very effective in capturing the nutrients needed by algae and limiting their growth.  However, many do not reproduce vigorously, so plantings should be as dense as possible.  In some situations, carbon dioxide supplementation and the use of plant food and iron might be useful.

Floating and emergent plants such as cattails and water hyacinth, lettuce, and lilies combat algae on two fronts – consuming nutrients and limiting light availability. 

If you are not ready to tackle aquatic plant gardening, you might consider using certain hardy terrestrial plants that thrive in water.  As long as their leaves can break the surface, peace lilies, pothos and aluminum plants will fulfill much the same role as true aquatic plants, and their root systems make for wonderful underwater effects.

Next time I’ll discuss how fishes, invertebrates and water additives can be used to combat algae.  Until then, please write in with your questions and comments.  Thanks, Frank Indiviglio.

Further Reading

To learn more about Cyanobacteria (“blue-green algae”), please see Aquarium Slime.

To read about adding beneficial bacteria to aquariums, please see my article Nutrafin Cycle.

3 comments

  1. avatar

    Kudos for touching on the use of aquatic plants for algae control! Most articles and blog posts about algae I’ve read fail to bring plants into the discussion, which is weird because plants and algae naturally compete for the same resources.

    Using aquatic plants has been my most effective method for managing algae levels in my tanks for years now. I’ve found that the key is to give plants a growth advantage by giving them access to nutrients that algae can’t get to. You mentioned allowing plants to grow emersed, which is a great suggestion since it gives plants access to CO2 in the air. I keep natural planted tanks so my rooted plants also have access to nutrients in the soil under-layer.

    Anyway, great post! For anyone looking for an easy aquatic plant to help w/ algae control, I recommend hornwort. It’s easy to find and doesn’t need to be planted.

    Cheers!

  2. avatar
    Savannah Oldham

    Is the best filter for removal of algae and keeping a 20 gallon tank clean a Below Gravel filter?

    Thank you

  3. avatar

    Hi Savannah,

    Undergravel filters can be very effective if properly set-up, but they will not remove algae.

    Best, Frank

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.