Ponds with soft, acid water may not respond to fertilizer. If the water does not turn green after six weeks of fertilization, then liming may be necessary. Ponds with waters of less than 20 mg/l of total alkalinity normally need lime. The lower the alkalinity level, the better the pond will respond to liming. Applying agricultural limestone will increase water hardness and alkalinity and decrease acidity. This will make the fertilizer more effective. Liming Materials
Agricultural limestone (calcium carbonate or dolomite), hydrated lime (calcium hydroxide) and quick lime (calcium hydroxide) are the most common liming materials for ponds. Agricultural limestone is not harmful to humans and will not cause high pH in water like the other forms of lime. It is the best and safest liming material to use in farm ponds.
A pond soil sample is needed to determine how much lime will be required. Collect samples from several locations evenly spaced across each pond, including both deep and shallow areas. Three to six samples per acre should be taken in ponds larger than 5 acres and at least 10 samples from smaller ponds. Samples can be collected easily in full ponds with a can attached to a pole. All individual samples should be mixed together and spread thin to dry. Dried soil samples should be pulverized, then placed in a soil testing box to be sent for analysis. Only about 2 cups of mixed soil are necessary.
Chemical analysis of pond soils can be conducted at the LSU AgCenter Soil Testing Laboratory for a small fee. Soil samples should be delivered to the Louisiana Cooperative Extension Service office in your parish for processing. Be sure to indicate “Fish pond” on the soil information sheet. Test results and liming recommendations will be mailed directly to you. Application Methods
New ponds can be limed before they are filled. Spread the liming material evenly over the dry pond bottom. A disk harrow can be used to mix the lime into the soil. In ponds with water, limestone should be applied evenly across the water surface. In small ponds, this may be done by spreading bagged limestone from a boat. In larger ponds, where several tons may be required, a platform can be built on the front of a large boat or between two boats tied together. Bulk limestone can be loaded (do not overload!) on the platform and distributed across the pond surface with a shovel. Even distribution across the entire bottom is essential for good results.
Do not apply limestone while a pond is being fertilized. Limestone settles phosphorus out of the water, making it unavailable to phytoplankton. Apply lime during late fall and winter. This will give it a chance to react with the acidic bottom mud before the spring application of fertilizer. Frequency of Liming
A liming treatment may last almost indefinitely in ponds with no outflow. Most ponds have some water discharge or are drained and refilled periodically. Most ponds with acid soils and moderate water outflow will probably need lime every three to five years. A method frequently used with good results is to apply the amount of lime recommended by a soil test, then apply one-fourth of that amount each succeeding year to keep lime requirements satisfied.