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photo of copper sulfate

Copper sulfate pentahydrate (hereafter referred to as copper sulfate) is an important tool for the catfish producer. As an EPA-approved algicide, copper sulfate is often an effective treatment for controlling algae in catfish ponds. Copper sulfate has several advantages compared to other options. Advantages include:

  • a relatively secure legal standing
  • no accumulation in fish
  • more economical than other copper-related products
  • typically gets tied up in pond sediments so very little leaves the pond
  • often very effective

To achieve control, farmers often have to use repeated small treatments to avoid toxicity issues with fish and the short persistence of copper in water. The effectiveness of copper sulfate and safety to fish are dependent on pond water quality. It can also be difficult to formulate a reliable treatment rate in ponds of unknown size and depth. Treatments are calculated in pounds per acre-foot, so the pond’s exact size and average depth must be known to formulate a safe treatment for fish.

Copper Products

There are additional copper products that are commercially available, including Cutrine®, K-Tea®, and several others. These products consist of copper housed in an organic complex available in both liquid and granular formulations, have longer persistence in water, and can be used safely in soft water. However, the much lower cost of copper sulfate makes it more appealing for use in large commercial-sized catfish ponds.

As with any other chemical, the product label should be followed and will provide instructions on the application of copper sulfate. One of the best methods to apply copper sulfate to a catfish pond is to weigh copper sulfate powder or crystals into burlap bags and then tow them behind a boat while the product dissolves. The product can also be weighed into cloth or burlap bags and placed 20-30 feet in front of paddlewheel aerators for a few hours until completely dissolved. The wave action generated by the aerators or when being pulled behind the boat are necessary to ensure the product is adequately dissolved to achieve an effective concentration in the pond water. Adding copper sulfate into the pond straight from the boat without allowing it time to dissolve will likely not adequately distribute the product throughout the entire pond.

Citric acid is often added to keep copper sulfate in solution longer. The ratio of copper sulfate to citric acid is 10:1, so if 50 pounds of copper sulfate are needed, 5 pounds of citric acid would be added. Most producers make a supersaturated solution of copper sulfate. Copper sulfate dissolves easily in water, but more copper sulfate can be dissolved if the water is heated. For example, at 32 oF, 0.33 pounds of copper sulfate can be dissolved in a gallon of water but heat the water to 212 oF and six pounds of copper sulfate can be dissolved. The easiest way to heat large volumes of water to the appropriate temperature is to use a water heater, like the ones used to heat the water in homes. These water heaters can be turned off when not in use to save energy.

Total Alkalinity

Total alkalinity is defined as the sum of titratable bases in water, which is mainly bicarbonate and carbonate for most pond water. Total alkalinity is typically measured as ppm as CaCO3. It can influence the toxicity of certain metals, such as copper, to fish. Calculating a pond treatment for copper sulfate is fairly simple. Table 1 provides a quick reference based on the widely known copper sulfate dose equation. From this table, it is easy to see that as total alkalinity is increased, so is the amount of copper sulfate that can be applied safely to the pond.

Maximum dose of Copper Sulfate (ppm) =  Total alkalinity (ppm) / 100

 

Example Calculation:  How many pounds of copper sulfate would be needed to treat a 10-acre pond that is 5 feet deep with a total alkalinity of 95 ppm?

Maximum dose of copper sulfate (ppm) = 95/ 100= 0.95 ppm

The total amount of acre-feet to be treated is 50 acre-feet (10-acre pond * 5 feet depth = 50 acre-feet)

1 ppm = 2.72 lbs/acre-foot, a conversion factor needed in the equation to change ppm to lbs/ acre-foot.

Knowing this information, we can now determine the amount of copper sulfate needed to treat the pond described in the example:

50 acre-feet * 2.72 lbs/acre-foot * 0.95 ppm =129.2 lbs of copper sulfate

Copper sulfate is a valuable tool available to catfish farmers for treating problematic algae blooms in ponds. Taking the time to determine the total alkalinity of your pond, as well as the average depth, will help ensure you are using a copper sulfate treatment that is effective at treating algae and safe for your fish. Feel free to contact the Alabama Fish Farming Center to test pond water alkalinity or if assistance is needed to calculate a copper sulfate treatment for your pond.

Copper Sulfate Pond Treatment Calculations

Max dose copper sulfate (lbs/acre-foot) recommendations based on total alkalinity (ppm CaCO3). Note: As total alkalinity is increased, so is the amount of copper that can be safely used in a pond.
Alkalinity (ppm)Treatment Rate (lbs/acre-foot)
511.4
681.8
852.3
1022.7
1193.2
1363.7
1534.2
1704.6
1875.0
2055.6
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