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Secchi Disk and Phytoplankton Bloom Management

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Monitoring and managing the phytoplankton bloom is important for recreational carp ponds. With time and experience, a pond manager will develop a visual sense about the bloom and respond accordingly. But due to differences in available sunlight and clouds, the appearance of the bloom changes and visual appearances can be misleading. A more reliable method of bloom measurement can be done with a Secchi Disk.

The Secchi Disk is a simple device that can be made at home that measures the water transparency or turbidity. It consists of an 8” diameter disk with a black-and-white design attached a pole or line with measurements. The disk is lowered into the water until it disappears and then raised until it reappears. These measurements are averaged to get the Secchi Depth.

For consistency, a Secchi disk measurement should always be taken in the same shady location and around the same time, between 9:00 a.m. and 3:00 p.m. This measurement does not provide an exact measure of transparency, because of errors due to the sun’s glare or differences in individuals eyesight, but it is an inexpensive and easily repeatable method to measure water clarity.

While the ideal Secchi Depth value will vary for each carp pond, a value between 18-24 inches is usually a good place to start. If the value is greater than 24” than fertilization might be advisable, while if less than 18” an application of an algaecide might be appropriate. Measurements should be recorded and over time can be compared to catch records to possibly determine fish activity patterns.Secchi Disk