Chlamydomonas, Chlorella, Euglena, Closterium, Anacystis spp., etc.
Mechanical/Physical Control Options
Floating, planktonic algae cannot be mechanically or physically controlled, except by replacing the pond water. Exchange of water from a well or other source that does not have an algae bloom will dilute the planktonic algae in the pond. This is not a practical option for most pond owners unless their ponds are very small and they have wells close by.
Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Aquashade, Blue Springs, and Crystal Blue are examples of non-toxic dye and other products are available. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.
Many types of mechanical removal devices are available that cut or chop up aquatic weeds. It is important to remember that many submerged plants regrow from fragments, so removal of cut fragments many be necessary to keep from spreading the unwanted plant. Companies that make cutters and rakes include but are not limited to Cutting Edge, Jenson Lake Mower, Midwest Aqua Care, and WeedRoller.
Physical barriers are also used to eliminate plants by shading the bottom. These work well for swimming areas, docks, etc. but must be kept clean of any buildup of sediment and debris. Lake Mat and Lake Bottom Blanket are examples of companies that makes these mats.
Biological Control Options
While many microscopic animals (zooplankton) eat planktonic algae there is no practical way to increase their populations, so no biological control is possible.
Chemical Control Options
The active ingredients that have been successful in treating planktonic include copper based compounds (E), sodium carbonate peroxyhydrate (G), alkylamine salts of endothall (G), and flumioxazin (G). E = excellent, G = good
Copper Sulfate or “blue stone” is probably the most commonly used algal treatments because of its availability and low cost. Copper sulfate comes in several forms depending on how finely it is ground. Smaller crystals will dissolve easier than larger crystals. In very hard water it is difficult to use copper sulfate because it binds with the calcium, precipitates out of solution, and renders the copper ineffective as an algaecide.
All copper compounds can be toxic to fish if used above labeled rates and can be toxic in soft or acidic waters even at label rates. Before using copper is it best to test the pond water’s alkalinity and adjust copper treatments to alkalinity concentrations. For additional information on using copper sulfate see the SRAC #410 – Calculating Treatment for Ponds and Tanks.
Cutrine Plus, K-Tea, Captain, and Clearigate are all chelated or compound copper herbicides that are effective on planktonic algae. Other chelated or compound copper formulations are available but are not linked to this web site.
GreenClean, PAK27, and Phycomycin are Sodium Carbonate Peroxyhydrate based herbicides. These are pelleted contact herbicides for control of blue-green algae. Hydrogen peroxide is the active agent in this algaecide. It is not effective on the macroalgaes, Chara or Nitella, or on any higher plants.
Clipper is a flumioxazin product and comes in a water dispersible granule which must be mixed in water first and then either sprayed or injected. It is a broad spectrum, contact herbicide. Contact herbicides act quickly. Flumioxazin should be applied to actively growing plants and a surfactant will be needed if the herbicide is applied foliage of floating or emergent plants. Water pH needs to be below 8.5 or flumioxazin will rapidly degrade and lose effectiveness.
One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.
One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.
Many aquatically registered herbicides have water use restrictions (See General Water Use Restrictions).
To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.
Planktonic algae can be promoted through fertilization. Fertilization will increase fish production in the pond by stimulating the natural food chain. However, over-fertilization can lead to planktonic algae blooms so dense as to promote dissolved oxygen depletions and fish kills, so fertilization must be practiced carefully. For additional information on fertilizing ponds see SRAC #471 Fertilization of Fish Ponds.