Koi Care Algaecide is a liquid algae-control product for use in ornamental fish ponds and water gardens containing live plants and fish.  Koi Care Algaecide controls many types of algae including “green water” blooms and filamentous algae. 

Can Koi Care Algaecide be used in a water garden containing live plants?

Yes. Koi Care Algaecide can be used in ponds containing submerged plants like cabomba, and floating plants such as water lettuce, and flowering plants, such as iris and water lilies. Koi Care Algaecide has been tested in extensive laboratory and field trials with aquatic plants. The following is a partial list of plants that we have tested and found to be compatible with Koi Care Algaecide when used as directed. 

Common name

Scientific name

Water lily

Nymphaea sp.


Canna sp.

Water lettuce

Pistia stratiotes

Water hyacinth

Eichhornia crassipes


Colocasia sp.


Nelumbo sp.


Typha sp.

Cardinal flower

Lobelia cardinalis

Fairy moss

Azolla caroliniana


Acorus calamus

Parrot’s feather

Myriophyllum aquatica

Pickerel weed

Pontederia sp.


Thalia sp.


Cabomba caroliniana


Egeria densa

Water pennywort

Hydrocotyle verticilliata

Can Koi Care Algaecide be used in a fountain?

Yes. Koi Care Algaecide can be used in ornamental fountains. Koi Care Algaecide is non-staining and non-corrosive. 

What types of algal problems will Koi Care Algaecide control?

Koi Care Algaecide is effective against “green water” (e.g., Chlorella) algal blooms. Dense populations of suspended algae cause green water algae blooms. The water may be so green that fish cannot be seen. Koi Care Algaecide also controls filamentous algae commonly known as “string” or “hair algae” (e.g., Cladophora) and “blanket weed” (e.g., Oedogonium). Algae growth in ponds can appear as green water blooms, filamentous algae on plants, and floating algal mats. Algae may also grow on rocks, fountains, and waterfalls.

  “Blanket weed” in a pond      “Green water” bloom in pond water  

How does Koi Care Algaecide work?

Koi Care Algaecide controls algae in two ways. Many algae, like Chlorella, consist of a single cell. Koi Care Algaecide causes the algae cell wall to leak. The algae respond much like a deflating balloon.  Other algae, such as Oedogonium, form filaments made up of many cells. Koi Care Algaecide binds to protein in the cell membrane, disrupting the flow of nutrients and ions across the cell membrane. Filamentous algae respond to Koi Care Algaecide by gradually disintegrating over time. Algaecide can be used with aquatic plants. 

Are Goldfish and Koi sensitive to Koi Care Algaecide?

Extensive laboratory and long-term outdoor field studies has shown that Koi Care Algaecide can be used in ponds containing Koi and Goldfish without worry. The outdoor field-testing ponds also contained a variety of other organisms including leopard frogs, tadpoles, snails and other aquatic life. 

Are there any precautions necessary when using Koi Care Algaecide?

Before using Koi Care Algaecide, make certain that the pond has vigorous aeration, i.e., a fountain, waterfall, or aeration device. Anytime dead algae are removed by the filter or settle to the bottom of the pond, the oxygen level may drop to harmful levels if adequate aeration is not provided. If adequate aeration is not provided, fish loss due to low oxygen levels may also occur. Therefore, when using Koi Care Algaecide in warm summer months, adequate aeration must be provided.  Do not shut pond pumps and aeration devices off at night. Be sure to keep the pond filter clean and running properly when using Algaecide. 

Do not use Koi Care Algaecide with crustaceans, including crabs, shrimp, freshwater shrimp, and freshwater lobsters. 

How do I treat with Koi Care Algaecide?

It is a violation of federal law to use this product in a manner inconsistent with its labeling. 

Add 1 teaspoonful (5 ml) of Koi Care Algaecide for every 50 US gallons (190 L) of pond/fountain water; 1 ounce per 300 gallons, 1 pint treats 5,000 gallons. 

Thoroughly mix Koi Care Algaecide into the pond/fountain water by adding it near the pump outflow, waterfall, or aeration device.  Koi Care Algaecide can be mixed in a bucket of pond/fountain water and dispersed evenly around the pond/fountain.  Repeat dose every 3 days until algae is controlled.  Be prepared to siphon out dead filamentous algae. Once algal growth is under control, add one dose per week. Weekly doses of Koi Care Algaecide will control algal growth and reduce pond/fountain maintenance.  

It is inexpensive at $17.50/pint, $27/quart, $39/1/2 gallon, $69/gallon.