Factors causing muddy water include watershed erosion, wave action, large populations of bullhead or carp, and livestock wading into the water. Correcting these problems by planting riparian vegetative buffer strips, using rotenone to remove undesirable fish, and fencing off livestock can allow the material to settle to the bottom of the pond. Placing a clear jar full of pond water on a shelf for one week can determine if settling will occur.
If the suspended particles are colloidal clay, they will not settle out. These tiny particles remain in suspension because of their microscopic size and the electrical charge surrounding their surface. In this case, a compound must be added to the water to correct the situation. Flocculating compounds such as aluminum sulfate (alum) and calcium sulfate (gypsum) work through a process that allows clay particles to combine into larger clumps, or “flocs”, that become large enough to sink out of suspension.
Alum is one of the most effective coagulants, but in low-alkalinity ponds can reduce pH to levels harmful to fish. In this situation, hydrated lime must be added with the alum to offset the reduction in pH. Gypsum is an effective coagulant in most ponds and does not cause a loss in alkalinity. Gypsum is also priced more economically, but application rates are greater when compared to alum. Do not use potting soil gypsum because this material contains a high proportion of inert (non-active) ingredients. Use the purest form of finely ground gypsum available, whether supplied in bags or bulk.
Pond owners should investigate the economic factors associated with purchasing, transporting, and applying these materials in addition to their pond’s unique water chemistry when deciding on a flocculent.
Flocculents should be applied only after the cause of the turbidity is corrected. Watershed protection and soil conservation practices should receive first attention. Successful clearing of water following an
application of alum or gypsum can be short-lived if exposed clay soils within the watershed continue to