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Treating Murky Ponds

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132-tons of gypsum will clear the lake.

We consider murky ponds a symptom to an underlying condition. Most ponds are clear. What causes some to be turbid? Here are standard procedures to diagnose the condition and make water appearance aesthetically pleasing.

The first step is determining potential sources for the problem. Is there:

  • A large population of carp, catfish, or other bottom feeders fanning up sediment?
  • Livestock frequently wading in the pond?
  • Wind action stirring sediment as waves roll across shallow flats?
  • Poorly vegetated shoreline.
  • Negative-charged clay soils at the pond site?

We narrow the list of possibilities by conducting a sediment test. Collect a water sample, preferably in a one-gallon glass jar. Place the container in a dark space for one week. When retrieving the jar, closely observe improvements in clarity and sediment on the bottom. If there is significant clearing, it’s assumed the source is one of the top four. If there is no change and the sample remains cloudy, unfortunately the problem relates to negative-charged clay particles in the soil. When this occurs, particles suspend in the water and are inhibited from settling to the bottom.

Two common methods to remove suspended particles are treating with ag gypsum or aluminum sulfate (alum). Alum produces fast results, but MUST be used by an experienced applicator. Improperly applied, alum may cause a sudden spike in alkalinity and kill fish. Please follow treatment procedures to the letter.

Gypsum is a safer product. To determine the correct amount, collect four, one-gallon glass jars of pond water and one jar of clear water. Leave one pond water jar as a control. Mix two level tablespoons of powdered gypsum into the clear jar. Stir into a slurry. Add the slurry into the three remaining samples–one tablespoon at a time. Each tablespoon represents approximately 80-pounds of gypsum per acre-foot of water.

Put 1-tablespoon in the first jar, two in the second, and three in the third. Wait at least 12-hours. Evaluate differences between jars. If there is no change, add another round of the slurry until one of the jars clears. Convert the number of tablespoons required to achieve clearing into total pounds (tons) of gypsum for treatment. Neither treatment is a guaranteed, permanent fix, but will improve clarity. Original conditions could return with the next significant influx of runoff into the pond.

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Preliminary clearing.

We recommend treating murky ponds with rock gypsum the size of a softball. Here’s a recent case study. Before vegetation developed around the shoreline, heavy runoff washed clay particles into the lake. Visibility was only 1-inch. To confirm our theory, we allowed the sediment test to sit 2-weeks. No change. We crushed a gypsum rock into powder and added 1-teaspoon to the water sample. Within 5-hours, the sample cleared.

Next step was converting the teaspoon application to tonnage required to clear the entire lake. Our biologist determined it would take 750-pounds per acre foot. Based on the lake’s surface acreage and average depth, the dirt contractor estimated the lake held 351-acre feet of water. Those numbers revealed it would take 263,250-pounds or 132-tons of gypsum.

Gypsum was stock-piled at strategic locations. A front-end loader was used to build 500 to 750-pound piles evenly spaced around the lake.  The top of each pile was just under the surface so water filters through it and disperses dissolved material throughout the water column.  Results vary with sediment density. Typically, improvement is visible in four to six-weeks.

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Shorelines must be well vegetated to prevent erosion.

This is a fascinating process. Don’t write-off a murky pond before completing above due diligence.

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