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Do I need to add lime to my pond?
STARKVILLE, Miss. -- Contrary to popular belief, fish don't like "clean" water.
If you have ever accidentally placed your pet fish in a bowl of pure, distilled water, you know what I mean. Fish have salts and other compounds in their blood. If their external environment is too different from their internal environment, fish have to fight continuously to keep the salts in and the water out.
If pond water is too pure, fish would be better off if you add agricultural limestone. Liming provides major benefits if you are growing sportfish in an area with acid soils. Limestone reduces the acidity of pond bottom soils, makes nutrients more available, and increases the alkalinity and hardness of water.
As a rule of thumb, if you need to lime your garden or food plots, you probably need to lime your pond. Liming is especially important if you plan to fertilize to increase fish production, as the fertilizer will not be utilized effectively in acidic waters.
Liming increases dissolved minerals in the water, which reduces stress on fish over the winter. Fish in acidic water with low alkalinity and hardness are more likely to get sick. In general, check to see if your pond needs liming once every five years to make sure it is adequate for fish.
The best time to lime is in the fall and winter. One reason for treating during the cooler seasons is that the limestone may cause a temporary drop in pond fertility by reducing phosphorus concentrations. Also, limestone dissolves slowly. Applications are best done well before the warmer months, which is the growing season for warm-water fish.
Extension Publication 1428 “Managing Mississippi Farm Ponds and Small Lakes” provides additional information on several common questions.
“How do I find out if my pond would benefit from agricultural limestone?” Contact your county Extension office to have the total alkalinity of your pond water tested. If it is below 20 milligrams per liter, liming would be beneficial to the fish population.
“How much agricultural limestone do I apply?” The lime requirement is determined by soil testing. In general, deficient ponds will need at least 1 ton per acre but sometimes more. Ponds in the Delta generally do not need lime. Ponds in the Black Belt and thick and thin loess soils need only 1 ton. Ponds in the red clay hills of north and central Mississippi often require 2 tons. Ponds in the sandy soils of south Mississippi usually need 2-3 tons.
“Is all lime the same?” No! Make sure to use only agricultural or dolomitic limestone in ponds with fish populations. Other forms (hydrated, slaked or quick) can be used to lime empty ponds before fish are stocked. If they are used in filled ponds, they cause the pH to increase dramatically, killing fish.
“How long will liming last?” An application of agricultural limestone typically lasts for three to four years, depending on the amount of water flow through the pond.
For more information on liming ponds, contact the local Extension Service office.
Editor’s Note: Extension Outdoors is a column authored by several different experts in the Mississippi State University Extension Service.