The water in a pond reflects the dirt in the pond and surrounding watershed. That is the main reason to have soil tested. That way you know what you are working with and a baseline is established. Then you know if it is acid or base and what elements may be in short supply or abundance. These type tests are usually done by Coop. Extension services and are inexpensive. You just note that it is for pond management purposes.Try this.

Kansas
Kansas State University Soil Testing Laboratory
2308 Throckmorton Hall, Manhattan, KS 66506
(785) 532-7897
www.oznet.ksu.edu/agronomy/SoilTesting/
Soil test cost: $8.50.
Includes: pH, P, K and organic matter.
To submit sample: Include name, address, and tests requested, and send to above address. Common regional problems: High pH in some areas, extremely low in others; soil may need sulfur or lime. Native soil may require additional P, K or organic matter.


In some situations a specific test may be suggested to deal with a particular problem. I have not heard of a test used for muddy water other than the jar test noted above. There is an entire area here on the topic and as Theo notes it provides for the use of the above methods.