Liming, or adding limestone to, ponds is used in order to increase the pH balance of the soil and water. When the pH balance of the pond falls too low, it reduces the success of fish reproduction. Liming improves the activity of fertilizer as well as several other water quality parameters. Liming is typically practiced in the southeastern states because of typical infertile soft water which are low in pH.
Check the pH of the soil before you decide on the specific lime to use, pH should be above 6.5 for fish health. Agricultural limestone is recommended by, Clemens University. Dolomitic lime is recommended but if high quality calcitic or calmag is available and the price is less, then they may be used instead.
Spread the lime evenly over the soil before filling the pond for the first time. Use a lime spreader to ensure that maximum coverage is obtained on the soil.
Flood the pond and check alkalinity and pH of the soil and water. Proper pH for fish health is between 6.5 and 9.0. Alkalinity should be 20 parts per million, pH should reach 8.6, the maximum that limestone will adjust the soil.
Re-lime every three years. Using a pontoon boat or barge, if required, (depending on the size of the pond), float the lime out and distribute evenly throughout the pond. Use a shovel to scoop the limestone over the edge of the boat or a portable water pump to spray the lime from the boat to the pond. If the pond is small enough, using a shovel from the edge of the pond will suffice to distribute the limestone. The weight of the limestone will carry it down to the bottom of the pond. Ensure at least 60 percent of soil is covered with the limestone. This process may also be used for liming a filled pond for the first time.
University of Florida: The Use of Lime in Fish Ponds
Clemens University: Liming Recreational Ponds