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Pond Algae Information

Last Updated: 4/18/12

The Effects of Algae on Pond Chemistry and Aquatic Plants
Algae Prevention
Algae Eaters - snails, tadpoles, shrimp, fish, plecostomus
Other Methods of Reducing Algae - by hand, algicides, dyes, coagulants, alum, Meridian mats, etc.
Algae Control in Large Ponds

Be sure to visit the main pond algae page for a ton more information!

The Effects of Algae on Pond Chemistry and Aquatic Plants

Information on how algae can affect the pH of ponds, the oxygen and carbon dioxide levels, pond pumps, and plants within the pond can be found at my pond algae information page.

Algae Prevention

All algae numbers can be reduced by reducing nutrients and/or light. Nutrient reduction results from feeding less, reducing fish concentrations, adding plants that take nutrients from the water, and installing a more efficient filtration system. Light can be reduced by providing shade with surface aquatic plants (water lilies, water hyacinth, duckweed, salvinia, azolla, snowflake, etc.) or artificial sunshades (suspended tarps or roofs). See my plant page for information on various pond plants.

Algae Eaters

This section includes information and links on snails, tadpoles, microorganisms, and plecostomus. Also, check out the algae-eating animals comparison table which covers both aquarium and pond algae-eating animals.

Hair Algae

Fish, insects, tadpoles, and snails do not prefer hair algae but they will eat a little if nothing else is available (like in late winter when hair algae grows well). There is no "good" algae eater for hair algae in ponds although a few snails could not hurt. But, one aquatic gardener says that rosy barbs work great! She moves them around in her aquariums to clean them out. They could be used in ponds in warm weather perhaps or in areas where the water is always warm. American flag fish are also said to eat hair algae but cannot survive below about 50 degrees F.

Surface Algae

While fish (especially fry) eat surface algae to some extent, it is best to introduce other animals to keep surface algae under control. The most common animals to add are snails and tadpoles. Go to my snail page for information on snails and my amphibian page for information on tadpoles. Some shrimp may also eat surface algae. Visit my shrimp page for more information.
Certain fish like grass carp (see my miscellaneous fish page) are also known for eating some algae but they usually also eat plants.

Plecostomus in Ponds:

Some people put plecostomus in their ponds. Because plecostomus cannot survive below 50-60 degrees F, they should not be added to ponds that get colder than this unless they are caught for the winter. Take note that plecostomus are one of the hardest fish to catch. It is said to be easier to catch them at night with a flashlight since they hide in debris asleep during the day. Also, in small ponds and tanks, plecostomus are known for sucking on goldfish and koi. Plecostomus may also be sensitive to salt added to ponds. They are reported to not be as damaging to plants in a pond versus an aquarium and do a good job at eating surface algae. See my plecostomus page for more information on them. A link specifically about keeping plecostomus in ponds (they think it is a good idea) can be found at To Pleco or Not to Pleco, that is the question!

At least one person does not agree that plecostomus cannot survive in cold ponds. While I have heard from many people whose plecos died in areas where the water goes below 50 degrees F, this is what one ponder had to say. As I have not put a pleco in any of my ponds, I cannot say firsthand about whether a pleco can adapt to the cold or not. I personally will not put one in my Zone 6/7 pond.
"Hi I ran into your website...and wanted to let you know about my personal experience I have with my pleco. He lives in my pond outside all year round and has survived the harshest winter one year we once had here in NY. You mention that plecostomus cannot survive below 50-60 degrees F on your web site. Although this may be factual by the books, my pleco has survived temperatures far lower than this. In fact, as of 3 years ago I added another pleco to the pond who also survived 3 winters since then. I think that their strength and ability to adapt to a new environment is underrated. So far I have noticed this fish to be the most adaptive and strongest of any aquarium type fish ever. I just wanted to let you know as your website is very informative and I think you should pass along as much information and other people's experience as possible. Great job on the site...."

Suspended Algae

Microorganisms eat suspended algae. Paramecium, daphnia, and other microorganisms should occur naturally in ponds but can be added in an attempt to reduce suspended algae concentrations naturally. See my miscellaneous pond animals page for information on these creatures and my pond catalogs page for information on where to purchase some if need be.

Other Methods of Reducing Algae

Here are some additional methods for controlling algae not mentioned in the other sections on pond algae.

Hair algae

Hair algae can be removed by pulling it off by hand while in or out of the pond. Using a long stick and twirling it around the algae allows some to be removed from on land. Barley straw may inhibit the growth of new hair algae. See suggestions under suspended algae as well as the methods of algicides, barley straw, and dyes will have some effect on hair algae.

Surface algae

Surface algae can be scrubbed off with abrasive pads but this only reduces the algae for a short time. In general, surface algae is good for ponds.

Suspended algae


Algicides can be added to kill suspended algae but they also kill some plants and animals, especially invertebrates. They should never be used in natural ponds for this reason. Algicides should only be used in a pond without plants or sensitive fish. There is a new product by Aquarium Pharmaceuticals called AlgaeFix which is supposed to be safe for fish and plants (but not for crustaceans and perhaps not mollusks either). I contacted them asking about it, and just got their report. It is supposed to kill all types of algae. It works very well at killing hair algae as well as other algae. Be sure to monitor the ammonia and nitrite levels and clean the mechanical filters often after a mass algae-killing.

UV Sterilizers:

UV sterilizers can be used to kill suspended algae. They will also damage or kill any microorganisms, bacteria, viruses, etc. that pass by the light. See my section on UV sterilizers for more information.

Barley Straw:

Barley straw can also be used to control suspended algae. See the barley straw page.


Various dyes such as Aquashade can be bought to dye pond water a transparent black. This effectively starves some of the suspended and submerged algae of light. Most of these dyes are not harmful and decompose over time. Since they do not last, they are not a long term solution to algae problems. The dyes may also deprive submerged plants, lilies, etc. from light and result in reduced growth or death. Dyes are best used in ponds that lack desired vegetation.


Various suppliers sell coagulants to clear up ponds. I have used Accuclear by Aquarium Pharmaceuticals. Adding these chemicals with polymers (plastics) causes minute pieces of algae, dirt, etc. to clump together. It does not affect most bacteria since they are too small. The clumps will then settle out or be filtered out if a filter is running. This effectively clears the water noticeably. Due to the expense, coagulants are only feasible for aquariums and ponds under about 500 gallons. The coagulant will not remove all algae, suspended solids, etc., so that by the next day or so, the algae will again grow and turn the pond green if conditions are right. For this reason, coagulants really are not a good choice for algae control. They are very good though at clearing due to suspended solids. One might use them after cleaning an aquarium or pond where lots of debris was stirred up. They work well for that. They also help when a lot of dirt gets into a pond after construction or a hard rain. Most coagulants are safe for most plants and animals if the instructions are followed.

Other Products

Meridian Mats:

There is a new product called Meridian mats that provides surface area for microbes, bacteria, etc. to grow. The technical services representative e-mailed me that the mats provide "the surface area in the water column for the proliferation of periphytic communities of algae and bacteria that in turn reduce macronutrients that are basically the cause of most problematic freshwater systems (excess P and N)." They look like large floss mats that you can put right in the pond. They are especially good for koi ponds which often lack plants. I have a small one. You can check out their web site at for more information.


Aquatic Ecosystems now sells Baraclear which is alum pellets to help clear up large ponds. I do not know much more about them yet. This is just another alternative.

Algae Control in Large Ponds

I get a lot of questions regarding algae in large farm ponds, fishing holes, natural water bodies, or other ponds that are bigger than the average hobbyist watergarden or fish pond. If anyone has any information on this topic (or any of my topics), let me know. Here are some of the recommendations I have for dealing with algae in large ponds (probably over 100,000 gallons or in the range of 1/4 to 20 acres or more (although costs go up with size)):

Pond Dealers Catering to Larger Ponds:
Aquatic Ecosystems
The Pond Guy
Zett's Tri-State Fish Farm & Hatchery - Sell plants and animals for larger ponds in bulk. Call 814-345-5357 for a free catalog.

More pond catalogs and details on the four above catalogs can be found on my pond catalogs page.

Also, see my farm pond page.

Pet Link Banner Exchange:

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Dutch Gardens, Inc. Discount Pond Supplies at

Go to the main plant page (full index).
Go to the aquarium algae index.
Go to the pond algae index.
Go to the aquarium plant index.
Go to the pond plant index.
See the master index for the plant pages (quick index).

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