I've had a number of calls recently from pond owners who want to begin control of algae in ponds. It seems that the algae is rising to the surface of the pond much earlier than normal this year. Each fall, as the strength of the sun diminishes, algae reduces the amount of photosynthesis taking place and it gradually sinks to the bottom of the water. As the sun strengthens during the spring, allowing photosynthesis to resume, the plants rise to the surface.
Too much algae in ponds can interfere with fishing, swimming, aesthetic value and irrigation. Copper sulfate (CuSO4) provides some of the best control for the dollar spent. However, the application method can influence how effective the product is.
Many times those who have used this product have expressed a lack of visible control after they'd used the product. But they've applied the CuSO4 in a manner that probably doesn't allow the greatest control. CuSO4 is available in either granular or liquid form. Granular is much cheaper than liquid, but you've got to get the granular converted to a liquid to get the best performance.
Using granular CuSO4, place 2-3 cups in a 2.5 gallon jug and fill with the hot water from your tap. Place outside in the sun and shake every couple of hours to mix. Not all the product will dissolve, but most will. With a pump up hand sprayer, on a day that the winds have pushed the algae to one side of the pond, apply to the algae. In 7-10 days you'll note a color change in the algae.
Wait until water temperatures are above 60 degrees before application. You'll need to reapply in about 30 days. Best not to apply during the warm summer months when water oxygen levels are lower, as any additional decaying plants could lower oxygen levels to the point where fish kill occurs. And never treat the entire pond, only a third or a fourth at a time, for the same reason as noted above with the concern of oxygen decline.
Lastly, remember you never want a pond devoid of vegetation as plants provide protection for young fish as well as provide oxygen. Consult the label for any restrictions on use, but many have zero or very few days between application and use. For more information on identification and control of aquatic plants: http://web.extension.illinois.edu/abhps/localfoods.html