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By Hans Peterson, Saskatchewan Research Council, Saskatoon
We're all familiar with the cattle, sheep and other animals that graze the land. In fresh water, such as your dugout, there are animals that do the same thing -- eat plants -- it's just that the plants in your dugout often can't be seen without a microscope. These tiny plants are called phytoplankton and can be algae or bacteria.
What animals eat these plants? The cattle and sheep of the water are called zooplankton and some of the most common ones are rotifers and daphnids. They have mouths and can have a tremendous appetite for the phytoplankton (see picture of zooplankton). A healthy population of zooplankton in your dugout is beneficial to the water. So, what should you be doing to support the zooplankton population in your dugout?
The number one reason that a dugout has a low level of zooplankton is found in overuse of pesticides such as copper sulphate. Copper effectively controls blue-green algae, but unfortunately zooplankton are also quite sensitive to copper. We therefore recommend that a dose of no higher than 2.5 lbs (1 kg)/0.5 million gallons be used. Some people believe that if 2.5 lbs is good 50 lbs must be better and throw a whole bag in the dugout. This is a sure way to kill all your zooplankton and you will get what we call "man-made algal blooms."
These man-made algal blooms consist of small green algae, and these blooms would not have formed unless the zooplankton were killed! The algae can tolerate high levels of copper and with everything else dead in the dugout all the nutrients are theirs!
So, when you use copper, use it only to control blue-green algae (by the naked eye these can be seen as clumps or clippings) and be careful not to overuse it. Think of your dugout as a living organism, and do what you can to foster the organisms that make the water quality better.
