Guide to Copper Sulfate for Ponds & Lakes (FAQ)

Ponds and lakes face significant challenges in sustaining a healthy ecosystem. In particular, lakes and ponds manmade or located near farmland or urban areas where there is substantial nutrient/pollution runoff and human impact are likely to, at some point or another, have algae growth.

The presence of some algae is natural and even necessary for proper ecosystem functioning. For example, some algal organisms, like diatoms, produce oxygen; as much as 40% of the oxygen that we breathe and depend upon for life is produced by diatoms. However, too much algae or the wrong type of algae (like filamentous algae and cyanobacteria) can wreak havoc, leading to decreased oxygen supply, green, scummy water, and possibly fish kills.

What is Copper Sulfate (Copper Sulphate) Used For?

One of the most popular and economical methods of controlling algae is a chemical product called copper sulfate. It’s also effective at treating areas for the organisms responsible swimmers itch, as well as parasites like leeches and ich. Copper sulfate contains copper as well as sulfur, and is available in crystal (or granular), liquid, and powder form. It’s water soluble so it breaks down quickly and easily when placed in water.

Historically, the antimicrobial properties of copper has been known for centuries – ancient Aztecs utilized copper compounds to treat skin infections and ulcers, and ancient Romans copper-containing ointments to treat wounds. While today these uses are not recommended or entirely backed up by science, copper sulfate is known to be quite effective in water treatment, ranging from controlling snails, aquatic weeds, algae, and bacteria. In 1956, copper sulfate was registered for use as a pesticide in the United States. It works by binding to the proteins in organisms, breaking down the cellular walls, and ultimately killing them. For this reason, while copper has historically been used to treat various ailments, copper sulfate should not make contact with your skin or be ingested. It’s considered toxic and can cause a variety of side effects.

Where to Buy Copper Sulfate?

Copper sulfate can be picked up from specialist retailers within the agriculture industry, or can be easily purchased online for extra convenience. After reading through the article to determine the correct dosage and application method, you can click below to see current prices for various crystal, liquid, and powder copper sulfate products in your location:

Copper Sulfate Application & Dosing For Ponds & Lakes

The dosage and application technique of copper sulfate depends upon the size of the water body, water alkalinity, the form of copper sulfate, as well as your specific goals and the organisms present in the water.

Granular/Crystal Copper Sulfate Application:

Crystal, or granular, copper sulfate should typically be dosed at five pounds per acre. Say, for example, that you have a one acre pond. You would mix 5 pounds of granular copper sulfate with 3 gallons of hot water, then spray it over half of your pond, wait a few days, and spray the other half. Never treat the entire lake or pond at once, as doing so will deplete oxygen levels while vegetation and algae decomposes after dying. You will need to adjust this dose depending on the brand of copper sulfate you are using – you don’t want to have more than 2.0 parts per million (ppm) in the water. Mixing the crystals with water prior to application simply aids in dispersing the product, and not dilution.

The solution can be mixed into the pond or lake using an agitator, or sprayed over the water with a broadcast spreader. With the latter method, wind direction and speed is key – you would not want to spray the chemical on a day with high wind speeds, or wind that is blowing away from the pond or lake. Applying on a relatively still, calm day is safest and most efficient. Crystal copper sulfate can be used to treat both surface as well as submerged algae and weeds, as the granules will sink to the bottom as they dissolve.

Liquid Copper Sulfate Application:

Liquid copper sulfate is more concentrated, and typically used when there are large quantities of algae. You will need to mix about 1 gallon of the liquid with 10 gallons of water, and this is good per one surface acre of water. The liquid variety only treats the first 1 to 3 feet of water, so is best suited to treating floating surface algae. Many of the liquid copper sulfate varieties are listed as not being safe for koi, goldfish, or trout ponds, so be sure to pay close attention the label before you purchase or apply it. In fish ponds, do not mix in more than .4 ppm of copper sulfate, or your fish may become ill or possibly die. This would be the equivalent of a quarter liquid ounce of the product per 275 gallons of water. Again, no more than one half of the lake or pond should be treated at a time. A larger water body, such as a pond, can handle slightly higher dosing, but again this depends on a variety of factors (such as the type of algae you’re trying to control) and you should pay close attention to the label, or contact a professional.

Liquid copper sulfate is best applied by using a broadcast sprayer. Within about 48 hours after application, the algae should be brown and dead or dying. You’ll need to remove the algae either manually or with a vacuum to prevent oxygen depletion. To disperse more directly and not worry about wind, you can use jets and hoses to inject it directly into the water.

Copper Sulfate Powder Application:

Copper sulfate powder, or dust, is very small and therefore easily distributed. The downside is there is much greater potential for it to impact other locations and organisms (including yourself!) as it’s carried on the wind effortlessly due to its tiny size. The powders are also easy to inhale on accident, and is moderately toxic, causing respiratory damage, gastrointestinal irritation and potential vomiting, and kidney and liver damage, among other things. The powder will need to first be mixed with water, and application options are the same as with crystal copper sulfate. Again, do not exceed a maximum of 2 ppm, depending on your water’s alkalinity (if the alkalinity is less than 50 ppm, don’t apply any copper products at all!).

When dry, copper sulfate is stable indefinitely. Once exposed to moisture, however, it of course begins to break down, and this is heavily influence by water temperature. The water should be above 60°F, but below 100°F, to ensure that the copper sulfate breaks down as normally as possible without releasing potentially harmful secondary compounds. If your water is below 60°, you’ll need to apply a greater dose of the chemical for it to work, as algae will be less responsive to the product below this temperature. Again, pay close attention to the product label!

Copper Sulfate Fish Toxicity – What Are Alternatives?

While copper sulfate is exceptionally effective in treating algae and aquatic weeds, there is potential for damage to wildlife as it is a toxic substance. Copper sulfate is, ironically, very toxic to fish, moderately toxic to birds, very toxic to invertebrates like snails, crustaceans, and insect larvae, as well as mammals if too much of the water is consumed or direct contact with the chemical is made. It’s highly water soluble, and should be used only in ponds and lakes that have liners that will prevent the chemical from leaching into the soil and thereby into other natural systems as well as drinking water.

Furthermore, if not mixed and diluted in water prior to application, copper sulfate will simply sink to the bottom of the water and bind to mud and substrate, where it will simply sit and either not help at all or suddenly release when conditions are right and cause damage since it won’t be controlled. Overall, this chemical is better suited to larger water bodies like lakes where it will be more diluted and cycled out more quickly than in small ponds where it has greater potential to be damaging.

Use Natural Control Methods:

Alternatively, you can control algae by a variety of more natural means. This includes hand raking and vacuuming, which can be time intensive depending on the size of the water body and the extent of algal growth, but will have virtually no adverse impact on the ecosystem. You can also utilize barley straw, which exudes a chemical as it breaks down that deters algal growth. It won’t, however, kill off any existing algae, so this is best used as a preventative method. Approximately one pound of straw for every 2,000 gallons of water will work just fine, making sure that you break apart and fluff up the straw so that water can still flow through it and not lead to water stagnation.

Other simple methods include incorporating more plants into your pond, which compete with algae for resources and space while also increasing oxygen supply. Some fish species (like plecos and Siamese algae eaters) are also known to consume algae and have been successfully used to treat slight to moderate algae issues while preventing future overgrowths. Another straightforward method is to utilize air pumps. These will incorporate oxygen into the water while also keeping the water moving; algae is able to thrive in still, low oxygen waters. Keeping oxygen levels to a minimum of 6 ppm will provide a healthy environment for your fish while also helping to minimize algal growth.