TECHNIQUES IN LIMING OF FISH POND.

Between the soil beneath a pond
and the water used to fill it. Clay
soils are often acidic. Because
ponds are commonly constructed on these soils, especially in the
southern and southeastern U.S.,
the effect on water quality can be
significant. Ponds with acidic
bottom soils that are filled with
poorly mineralized water characteristically have low
alkalinity and hardness. When total
alkalinity and hardness are below
20 mg/L (as CaCO3) pH and productivity are usually reduced.
Alkalinity concentrations below 20
mg/L often lead to large swings in
daily pH values, which stress
aquatic animals. Acidic soils
contain high concentrations of hydrogen ions and/or aluminum
relative to the concentrations of
calcium and magnesium, which are
important minerals for good water
quality. The acidity of pond soils can be

neutralized and the productivity of
the pond improved by liming.
“Liming” refers to the
application of various acid-
neutralizing compounds of calcium, or calcium and magnesium. Liming
ponds has three important
benefits. Liming may enhance the
effect of fertilization. Liming helps
prevent wide swings in pH. Liming
also adds calcium and magnesium, which are important in animal
physiology. The difference between
alkalinity and hardness It is important to understand the
difference between alkalinity and
hardness. These two aspects of
water chemistry are often
confused. The misunderstanding
relates to the term used to report them – as ppm CaCO3 (mg/L). Total alkalinity indicates the entire
quantity of titratable bases present
in water, primarily bicarbonates,
carbonates and hydroxides. The
most important components of
alkalinity are bicarbonates and carbonates. Hardness is the overall
concentration of divalent salts
(calcium, magnesium, iron, etc.)
but does not identify which of
these elements is/are the source of
hardness. Calcium and magnesium are the most common sources of
water hardness. Liming increases
both alkalinity and hardness. The effect of liming on
fertilization Both recreational and commercial
ponds are often fertilized to
improve fish production.
Fertilizers containing nitrogen,
phosphorus and potassium
(especially phosphorus) stimulate the growth of microscopic plants
(phytoplankton) and animals
(zooplankton), which, in turn,
serve as food for animals in the
aquatic food chain. In recreational
ponds, an abundance of plankton supports larger populations of
species such as largemouth bass
and bluegill. In ponds used for
commercial production of juvenile
fish, plankton is the primary food
source. Healthy phytoplankton blooms also absorb toxic nitrogen
wastes and raise daytime dissolved
oxygen concentrations, so they are
important to water quality. Perhaps the most common reason
to lime ponds is to improve the
response to fertilization. In ponds
built on acidic soils and filled with
fresh water of low mineral content,
much of the phosphorus added in fertilizers becomes tightly bound in
pond sediment where it is not
available to support phytoplankton
growth. Proper liming can
improve phosphorus availability
and greatly enhance pond productivity. Liming and pH swings In ponds with acidic soils filled with
poorly mineralized water with low
total alkalinity, liming will increase
total alkalinity. This helps stabilize
pH, which can swing widely from 6
to 10 during the day if total alkalinity is below 20 mg/L.
Fluctuations in pH are the result of
the interplay of photosynthesis
and respiration. Nighttime
respiration increases CO2 concentrations, creating carbonic
acid and causing pH to fall. During
the day phytoplankton absorb CO2 for photosynthesis, causing pH to
rise. Large, daily changes in pH can
stress aquatic animals (Fig. 1).
Most aquaculture species can live in
a broad range of alkalinity
concentrations, but the desired alkalinity for many animals is 50
mg/L or higher. Liming to raise
total alkalinity to the required or
preferred ranges buffers the water
and reduces swings in pH (Fig. 2). Liming and hardness Hardness concentrations are
important to aquatic animals also.
Calcium and magnesium are
essential for bone and scale
formation in fish. The most critical
component of total hardness, however, is the calcium
concentration or “calcium
hardness.” Environmental
calcium is crucial for
osmoregulation, the biological
process that maintains precise levels of internal salts for normal
heart, nerve and muscle function.
In low-calcium environments,
animals can lose (leak) substantial
quantities of these salts into the
water. Calcium is also important in the molting process of shrimp and
other crustaceans, and can affect
the hardening of newly formed
shells. Most aquatic organisms can
tolerate a broad range of calcium
hardness concentrations, but a desirable range is 75 to 250 mg/L
with a minimum concentration of
20 mg/L. Adding liming materials
or gypsum increases hardness. Deciding whether to lime a
pond To determine whether a pond
needs to be limed, first check total
alkalinity. Collect a water sample
from the first several inches below
the surface, making sure the
sample contains no bottom sediment (mud). Collect the
sample in a clean quart container
that has no chemical residues. The
sample can be tested for total
alkalinity with a swimming pool
test kit. Or, the sample can be sent to a university laboratory or
commercial testing company.
Check with your county Extension
agent for information about water
testing. If the total alkalinity of the water
sample is less than 20 mg/L, the
pond may benefit from liming. The
amount of lime needed depends on
the chemical characteristics of the
bottom sediment. Take samples of the pond bottom and have them
analyzed to determine the soil pH
and the amount of liming material
to apply. Collect the samples as
you would for cropland. Take
samples to a soil depth of 6 inches from several locations in the pond
(an S-shaped pattern is typically
used). In ponds less than 5 acres,
collect at least ten samples per
acre. In a new pond, collect soil
samples before filling. In ponds with water, push a length of PVC
pipe into the bottom and remove
the mud plugs from the pipe. Or,
attach a can or small container to a
long pole and scoop soil from the
pond bottom. Combine the samples, mix them evenly, and
spread the blended sample out to
dry. After drying and crushing,
mark the sample “pond mud”
so the appropriate analysis can be
made. Approximately 1 pint of dried, blended soil sample is
needed for lab analysis. Contact
your county Extension agent for
information about soil testing
services. In some areas, specific tests for
“pond mud” are not available.
However, there is a simple and
reasonably accurate way to
estimate the amount of liming
material needed in a pond. Submit the sample and request the
recommendation for alfalfa
production. The amount of liming
material needed to grow alfalfa
will be very close to the minimum
required for producing most aquatic animals. Another method
is to apply 1 ½ to 2 times the
amount of liming material used to
farm row crops in the surrounding
area. Choosing liming materials Materials such as agricultural
limestone, basic slag, slaked lime,
quick lime and liquid lime have
been used to lime ponds. While all
these compounds neutralize soil
acidity, some are more practical or effective than others. It is not advisable to use quick lime
(CaO) or slaked lime (Ca(OH)2). They are more expensive and can
cause pH to rise rapidly to levels
that can harm aquatic life. Basic slag is a satisfactory liming
material, but it is not commonly
available and its effectiveness may
vary significantly from load to
load. A substance known as silicate
slag is not an acceptable material and should not be used to lime
recreational or commercial
production ponds. Liquid lime is popular among some
farmers. This product is made by
suspending finely powdered
agricultural limestone in water.
The small particles react more
rapidly with the acid in soil and water and produce quick results.
However, because this mixture is
half water, it takes twice as much
liquid lime as agricultural
limestone to achieve the same
results. Liquid lime can cost much more than agricultural limestone. Finely crushed agricultural
limestone is usually the best
material to use. It is cost-effective
and readily available. Both pond
alkalinity and hardness can be
increased by adding either CaCO3 (calcitic) or CaMg(CO3)2 (dolomitic) limestone. It is difficult to add too
much agricultural limestone to a
pond. At a pH of 8.3 or greater,
calcium combines with carbonate
to form limestone and drops out of
solution. Limestone does not dissolve well in ponds where soil
acidity has been neutralized and
water pH has stabilized at or above
8.3. Neutralizing value and
efficiency Commercial liming materials vary
in their ability to neutralize soil
acidity – their neutralizing value
(NV). Pure calcium carbonate is the
standard used for assigning
relative neutralizing values to each of the liming compounds. Calcium
carbonate is considered to have an
acid neutralizing value of 100
percent. Agricultural limestone
may have NV values between 85
and 109 percent depending on its specific chemical composition.
Slaked lime has an NV of 136
percent. Neutralizing values for the
liming materials previously
discussed may fall between 55 and
179 percent (Table 1). Table. 1. Common names,
chemical names and
neutralizing values (NV) of
several liming materials. Common Name Chemical Name NV (%) Basic Slag -- 55-79 Calicitic Limestone Calcium Carbonate, CaCO3 85-100 Dolomitic Limestone Calcium Magnesium Carbonate,
CaMg(CO3)2 95-109 Slaked or Hydrated
Lime* Calcium Hydroxide, Ca(OH)2 136 Quick or Burnt Lime* Calcium Oxide, CaO 179 *Use of these materials is not
recommended because their effects
on pH can be harmful to aquatic
life. Finely crushed agricultural
limestone is composed of different
sizes of particles. Small particles
react faster and dissolve more
rapidly and completely than large
particles. Therefore, the neutralizing efficiency (NE) of
agricultural limestone depends on
the fineness of the mixture. The
particle fineness and associated
neutralizing efficiency are
determined by passing limestone through a series of sieves. Particles
that pass through a 20-mesh sieve
but that are retained by a 60-mesh
sieve have an NE of 52.2 percent.
Those passing through a 60-mesh
sieve have an NE of 100 percent. The various quantities of each
particle size grouping and their
associated NE values must be
averaged to arrive at an overall NE
rating. If the liming requirement,
neutralizing value (NV) and
neutralizing efficiency (NE) are
known, it is possible to calculate
the precise amount of lime
needed. Divide the amount of liming material recommended
(tons per acre) by the product of
the neutralizing value and the
neutralizing efficiency (NV x NE). For example, a farmer submits a
soil sample and the analysis
indicates that 3 tons per acre of
pure calcium carbonate are
required to neutralize the pond soil
acidity (or to produce alfalfa). The agricultural limestone available at
the local farm supply store has an
NV of 85 percent and an NE of 71
percent. The amount needed is
determined as follows (percent
must be converted to a decimal first). Tons/acre CaCO3 divided by (NV multiplied by NE) = tons of
limestone needed.
3.0 ÷ (0.85 x 0.71) = 4.97 tons of
limestone needed. When only one value is available
(NV or NE), divide the tons
recommended by that value. For
example, if only the NV (85
percent) is known:
3.0 ÷ 0.85 = 3.53 tons of limestone needed. Timing and application of liming
materials To be effective, liming materials
should be applied evenly over the
bottom of the pond. The best, and
easiest, time to lime a pond is
before it is filled with water. A
liming truck or tractor-pulled liming wagon can be driven
around in the dry pond to spread
the lime evenly over the entire
bottom. It is not necessary to disc
the lime into the soil, but this will
accelerate its neutralizing activity. If the pond contains water, lime
should be applied evenly over the
entire pond surface. Lime is loaded
onto a boat or barge and then
shoveled or washed uniformly into
the pond (Fig. 3). Often a sheet of plywood can be attached across
the front of one or two small boats
and the lime placed on the
plywood. Lime is heavy and
shoveling it is tedious. Therefore,
some pond owners hire professional companies with liming
barges to spread the lime. For
small ponds of less than 1 acre,
liming trucks can be backed up to
the edge of the pond and the lime
distributed with the spreader on the truck. This method works best
if the truck can move around the
entire pond and broadcast the lime
evenly. Fig. 3. Agricultural lime being distributed evenly over a
pond from a pontoon barge. Agricultural lime does not dissolve
quickly in water and will sink to the
bottom. Liming a pond filled with
water has an immediate effect on
water quality. It increases pH,
reduces soluble phosphorus, and reduces free carbon dioxide.
Increasing the pH may cause the
water to clear of suspended
particles (mud), which can help
pond productivity by increasing
the light available to plants. However, liming a pond shortly
after fertilizing may remove
phosphorus from the water, which
could prevent a phytoplankton
bloom from developing.
Recreational ponds are typically fertilized in the spring with
compounds containing
phosphorus. So it is usually best to
apply lime in fall or winter when
productivity is unlikely to be
affected. The pond will equilibrate within several weeks and then
fertilizer can be applied to adjust
productivity. Limestone dissolves slowly over
time. Alkalinity and hardness are
washed out of the pond with
overflow and drainage water.
Ponds that require lime usually
need repeat treatments every 3 to 5 years. Alternatively, annual lime
applications can be made using
one-fourth the original
recommendation to maintain
alkalinity, hardness and pH at
acceptable levels. If a pond needs lime, it will not respond well to
fertilizer. Managing calcium hardness If the alkalinity concentration is
below 50 mg/L, agricultural
limestone can be used to increase
alkalinity and hardness. If total
alkalinity is above 50 mg/L, adding
agricultural limestone will not be effective. Similarly, if pond pH is
stable at 8.3 or greater, limestone
will not dissolve. For several
aquaculture species (e.g., striped
bass, red drum and crawfish), the
preferred concentration of calcium hardness is above 50 mg/L. Liming with agricultural limestone,
using recommendations based on
soil analysis, will usually increase
alkalinity and hardness to the
minimum required concentration
of 20 mg/L. A low total hardness value is a reliable indication that
the calcium concentration is low.
However, a high hardness value
does not necessarily mean that the
calcium concentration is
high. Where hardness is caused by CaMg(CO3)2 (dolomitic limestone), the total hardness value reflects a
mixture of calcium and
magnesium. Magnesium can
represent as much as 50 percent of
the hardness produced by CaMg
(CO3)2. Other magnesium-containing
compounds, such as magnesium
sulfate, may be the source of
hardness in high alkalinity
environments. Therefore,
agricultural limestone may not always raise calcium to the
required or minimum desired
concentrations. Agricultural
gypsum (calcium sulfate) or food
grade calcium chloride may be
needed to raise calcium hardness in waters with alkalinities greater
than 50 mg/L and low hardness.
Where alkalinity is high and
hardness is caused by magnesium,
adding agricultural gypsum or
calcium chloride is also an effective way to raise the calcium
concentration. Alternative materials for raising
calcium hardness Agricultural gypsum (calcium
sulfate). Calcium hardness and
total hardness can be increased
about 1 mg/L by applying 5
pounds of agricultural gypsum per
acre-foot. Adding 125 pounds of agricultural gypsum per acre-foot
would raise hardness
approximately 25 ppm. Calcium chloride. Calcium hardness
and total hardness can be
increased about 1 mg/L by
applying 4 pounds of calcium
chloride per acre-foot. Adding 100
pounds of calcium chloride per acre-foot would raise hardness
roughly 25 ppm. It is important to note that if
phosphorus is added to ponds
immediately before or shortly
after applying gypsum or calcium
chloride, the phosphorus may
combine with calcium. This may cause both elements to drop out of
solution as calcium phosphate.
Phosphorus-based fertilizers
should not be added for several
weeks before or after the
application of compounds that increase calcium hardness. If high volumes of water regularly
flush through a pond, the
agricultural limestone, agricultural
gypsum or calcium chloride that
have been added can be washed
out. Often more than the recommended amount of
limestone or gypsum is added so
the materials will not have to be
applied as often. These chemicals
will not cause problems in a pond if
added at two or three times the calculated amount. Culturists often overlook the
importance of hardness and
alkalinity. The pond environment
and aquatic animals benefit from
water that has the desired levels of
alkalinity and hardness. The minimum concentration for both is
20 mg/L. Managing these two
components of pond water
stabilizes or buffers pH
fluctuations, improves the
availability of phosphorus for phytoplankton, increases the
natural food in ponds, and
provides calcium for
osmoregulation, egg hardening
and other metabolic needs. Water
should be tested periodically so that hardness and alkalinity can be
managed properly. Apply liming
materials as needed and keep good
records to improve water quality
and overall pond productivity.

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