Management of water quality for fish

Material Information

Management of water quality for fish
Series Title:
Circular Florida Cooperative Extension Service
Rottmann, R. W
Shireman, J. V
Place of Publication:
Gainesville Fla
Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences
Publication Date:
Physical Description:
18 p. : ill. ; 28 cm.


Subjects / Keywords:
Fish culture -- Water-supply ( lcsh )
Fish ponds -- Florida ( lcsh )
Water quality management -- Florida ( lcsh )
Fish ( jstor )
Oxygen ( jstor )
Ponds ( jstor )
government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )


Circular (Florida Cooperative Extension Service) ;
Statement of Responsibility:
R.W. Rottmann and J.V. Shireman.

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University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
19327533 ( OCLC )


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Copyright 2005, Board of Trustees, University
of Florida


Management of rr7
Water Quality
for Fih R. W. Rottmann and J. V. Shirean

*t "I' /

Management of Water Quality for Fish

R. W. Rottmann and J. V. Shireman

R. W. Rottmann is a Biological Scientist III and J. V. Shireman is Chairman, Department of Fisheries and
Aquaculture, Institute of Food and Agricultural Sciences, University of Florida.

Table of Contents

Introduction ...................................... ................... ... .......... 1
Chemical Factors
D dissolved O oxygen ........................... ....................... ................. 1
Detection of Oxygen D epletion .. ....................................... ............. .. 1
Emergency Treatment for Oxygen Depletion ............... ........................... 2
Supplem ental A eration .................. .................. ...................... 3
Carbon Dioxide ............ ...... ................... ......................... 5
N nitrogen ................... ................ ................... .. ...... 6
Hydrogen Sulfide .................. .................. ................... .... 6
A cidity ............ ......... ................... ................... .... 7
A lkalinity and H ardness ................. .................................. ... 7
Ammonia ........ ....................................... 8
N itrites ............... ........ .................. ................... .... 8
Ammonia and Nitrite Removal ............................................ ..... 9
Physical Factors
Temperature .................................................................... 13
Turbidity .......................... ......... ...................... .......... 13
Fertilization ................... ....................................... 14
P on d R en ov ation ........... ............................................................ 15
Determining Pond Dimensions for Treatment ......................................... 15
Summary ............... ....................... ..................... .......... 16
Appendix: Useful Tables and Conversions ............................................... 16
Conversion Factors .................. .................................................. 16
Pounds to Add to Obtain Desired Concentration ................ ...................... 17
Grams to Add to Obtain Desired Concentration ........................................ 17
Conversion of V olum e U nits ............................................................ 18
Conversion of Length Units .......................................... ........ 18
Conversion of W eight Units ........... .. .. .................................. 18

Water, although the most important component
for raising fish, is often the most neglected factor.
Fish are totally dependent on water: they derive oxy-
gen from it, they ingest it, they excrete their wastes
into it, they take it up and lose salts into it, and they
are in perpetual contact with it. Poor water quality
can cause massive fish kills and is often the major
factor contributing to fish diseases. Instead of add-
ing chemicals to the water to treat a disease out-
break, the fish culturist should first look at water
quality to determine why the outbreak occurred.
Water quality does not remain constant. In ponds,
it can change dramatically over a few hours. Even
water from deep wells and springs can change over
time. It is not a simple matter for the fish farmer or
pond owner to assess water quality. The fisheries
manager must use chemical tests as well as observa-
tions to detect changes.
The purpose of this publication is to assist the
Florida fish farmer or pond owner in pond manage-
ment. The text Water Quality Management for Pond
Fish Culture authored by Claude E. Boyd (Elsevier
Science Publishing Co., Inc., New York) is an ex-
cellent source of more detailed information on the
subject and is recommended reading. This circular
provides a simpler approach and addresses certain
aspects of water quality specific to Florida not
covered in Boyd's book.

Chemical Factors
Dissolved Oxygen
Dissolved oxygen is by far the most important
water quality factor for fish; fish cannot live without
it, and oxygen depletion probably results in more fish
kills than all other factors combined. Concentrations
of oxygen are expressed as parts per million (ppm)
by weight or milligrams/liter. The amount of oxygen,
as well as many other gases that can be dissolved in
water, decreases with higher temperature; at 680F
water can hold 8.8 ppm oxygen, while at 900F,
saturation is at 7.3 ppm. In combining this relation-
ship with the increased demand for oxygen by fish
and other organisms at higher temperatures, one can
readily see why summer oxygen depletion is so
prevalent. Fish farmers, in an attempt to maximize
production, stock a greater biomass of fish in a given
body of water than that found in nature. As a result,
there is a greater demand for oxygen by the fish in
production ponds.
Oxygen requirements for fish vary according to
species, age, and culture conditions. Most warm
water fish require a minimum of 1 ppm to survive
and more than 4 ppm for growth, reproduction, and

good health. Early life stages usually require greater
oxygen concentration than needed by adults.
Chronically low dissolved oxygen causes stress,
thereby increasing the chance of infectious diseases.
The major sources of oxygen in water are direct dif-
fusion at the air-water interface and plant photosyn-
thesis. There are many consumers of oxygen in a
pond, including fish, insects, bacteria, and aquatic
plants. While plants are oxygen producers during the
day, at night they become oxygen consumers. In
ponds and lakes, a balance usually exists between
oxygen produced and oxygen consumed. A number
of things can upset this balance resulting in oxygen
depletion and subsequent fish kills. These include:

1. Increased organic waste entering the water.
Any organic material such as manure from
feedlots, septic tank waste, and excess fish feed
increases the oxygen demand in the water. The
decay process of these materials consumes
2. Die-off of aquatic plants. Because aquatic
plants are the primary source of oxygen in
ponds and lakes, any sudden death whether by
herbicides or natural causes can result in oxy-
gen depletion. The problem is further com-
plicated by increased oxygen consumption by
the decay of this plant material.
3. Excess aquatic plants. Plant growth (especially
phytoplankton and submersed plants) during
warm months may produce more oxygen than
can be held in solution (supersaturation). Oxy-
gen demand by the plants during evening
hours is also great resulting in wide fluctua-
tions in dissolved oxygen during a 24-hour
period. Reduced light intensity caused by
several days of overcast weather limits oxygen
production while oxygen consumption remains
high. The result is oxygen depletion and fish
4. Temperature stratification of pond water and
the eventual remixing (turnover). This problem
is discussed later under "Physical Factors:

Detection of Oxygen Depletion
Oxygen concentrations in a pond almost always
fluctuate during a 24-hour period; the highest con-
centration usually occurs during mid to late after-
noon and the lowest concentration is observed just
before dawn. Early morning hours are therefore the
most critical. An oxygen meter or chemical test kit
is the best way to detect dissolved oxygen depletion.

Ideally, dissolved oxygen concentration should be
measured during the late evening or early morning.
When this is impractical, it is impossible to estimate
the potential for oxygen depletion by measuring oxy-
gen in the early evening and again two or three hours
later. Oxygen respiration is considered to be a
straight line; therefore, these two values can be plot-
ted on graph paper against time during the remain-
ing hours of darkness to predict the dissolved oxygen
at dawn. Figure 1 illustrates this method.
When a meter or test kit is unavailable, the follow-
ing observations and conditions can be used to an-
ticipate oxygen depletion.
Fish swim at or near the surface or gulp for air
during late night or early morning. Fish may
return to deeper water later in the day.
Fish suddenly stop feeding.
There is a rapid change in water color to brown,
black, or gray.
A putrid odor arises from the water.
There is loss of algal bloom.
There has been an extended period of hot cloudy
There is a heavy summer wind and rain storm.
Emergency aeration should be applied whenever
fish show signs of oxygen depletion or when dis-
solved oxygen drops below 4 ppm.

Emergency Treatment for Oxygen Depletion
The most effective treatments for oxygen depletion
are mechanical aeration and freshwater flush.
Whichever method is used, it will be more effective
if 1) treatment is started as soon as possible, 2) the

Measured values

\ Projected value

5 pm

10 pm

5 am

Figure 1. Estimation of potential for dissolved oxygen

greatest possible volume of water is sprayed or
agitated, and 3) a water current is established in the
pond. It is important not to disturb the bottom mud,
which contains large amounts of organic matter and
bacteria that will contribute to the oxygen depletion
problem if mixed with the water.
Paddle wheel aerator: These are powered by farm
tractors and are widely used by fish farmers (Figure
2). These aerators provide a large amount of oxygena-
tion per unit and are relatively inexpensive, fairly
durable, mobile and easy to operate. The trailer-
mounted aerator consists of two paddle wheels at-
tached to the axles of a truck differential and set
perpendicular to a drive shaft connected to the power
take-off (pto) of a tractor. The pto turns at 540 rpm;
because of the gear reduction in the differential, the
paddle wheels turn at 120 rpm. The two wheels are

Figure 2. Emergency paddle wheel aerator.



Trailer wheels

Tractor hitch

18 inches in diameter; 12 paddles, each 8-12 inches
long and 6 inches wide are attached to each wheel.
Paddle depth in the water should be about one-half
the length. Paddle wheels should turn toward open
water. The paddle wheels splash water into the air
and produce a current behind the aerator. In com-
parison tests, paddle wheel aerators were among the
most effective of all emergency aerators evaluated.
Large volume pumps: Airmaster* and Chrisafulli
pumps are also widely used for emergency aeration.
These are large, trailer-mounted, tractor-powered,
centrifugal pumps with a sprayer device fitted on the
outlet. Comparison tests indicate that the Airmaster
pump is nearly as efficient as the paddle wheel
aerator. However, the Chrisafulli pump was only
about half as efficient as either the paddle wheel or
the Airmaster.
Outboard motor: These can be used to produce a
water current if run in a fixed position. However,
driving a boat with an outboard motor in the pond
is practically useless for aeration.
Water replacement: A freshwater flush is very ef-
fective for emergency aeration. The inlet pipe should
be equipped with an aeration device. Tests have
shown that a half-open gate valve or a slotted cap
are most efficient for adding oxygen.
Chemical treatment: The following treatments can
be used to help counteract oxygen depletion.
However, chemicals are not as effective as
mechanical aeration or freshwater flush. Any of the
chemicals listed below may help, but best results are
expected when they are used in combination.
Treat water with 6-8 lb of potassium per-
manganate per acre-ft as soon as the problem
is observed. Treat again with half the above rate
if the purple color disappears within one hour.
Potassium permanganate does not add oxygen
to the water but reduces the oxygen demand of
the organic chemicals in the water.
At midday, add 50 to 100 lb of triple super
phosphate per surface acre to stimulate plants
to produce oxygen. This treatment should not
be used when excess plant growth has caused
the oxygen depletion.
At dusk, add 30-50 lb of hydrated lime per acre
to tie up CO2 (see "Carbon Dioxide") in the
water, allowing the fish to better utilize the oxy-
gen present.
Supplemental Aeration
Unlike emergency aeration which is used to correct
oxygen depletion once it has occurred, supplemental

*Use of tradenames does not constitute product

Figure 3. Supplemental paddle wheel aerator.

methods are used to prevent oxygen depletion from
occurring. Supplemental aerators use small electric
motors to operate paddle wheels, air blowers, pumps,
or impellers continuously. Aerators that create a
water current, as well as splashing, spraying, or in-
jecting air into the water, are the most efficient. Pad-
dle wheel aerators are used widely in Japan and Israel
(Figure 3). Recent tests have shown that propeller-
aspirator aerators are efficient (Figure 4). Airlift
aerators supplied with air from a regenerative blower
are used in ponds for ornamental tropical fish and
striped bass. Airlift aerators powered by a
regenerative blower have several advantages for
Florida aquaculture: 1) airlifts are simple and inex-
pensive to build and require little maintenance; 2)
airlifts create a mixing current in the pond water as
well as injecting air; 3) regenerative blowers provide
greater volume of air/unit power compared to other


Figure 4. Propeller-aspirator aerator.

types of compressors; 4) a single blower will provide
aeration for many ponds, thereby reducing motor
maintenance; and 5) the blower has only one moving
part and the motor can be isolated from the corrosive
influence of the water, further reducing maintenance.
Several designs of airlift aerators are illustrated in
Figure 5.

Airlifts can also be used for pumping water in
situations where the height of the lift is not too great.
An airlift is essentially a vertical pipe submerged in
water with air injected near the bottom. As the bub-
bles rise in the pipe, a mixture of air and water is pro-
duced that is lighter than the water outside the pipe.
The heavier water enters the lower end of the pipe.


Plastic tee

Air supply-

----- Plastic ell

Pond or
tank bottom

2" x 4

Air supply -

Direction of
water flow -

Air supply

Plastic cap
with holes.,

I Ii

Figure 5. Airlift aerators.

-- Plastic ell

-L-shaped brackets

As long as air is injected, the air-water mixture spills
out the top of the pipe.
The main factor affecting the efficiency of the
airlift is the percentage of submergence (see Figure
6). This can be calculated by the following formula:
% Submergence = submergence!submergence+total liftX100
The relationship between percentage of
submergence, diameter of lift pipe, and flow rate is
presented in Table 1. Maximum flow rate and mix-
ing current are obtained at 100% submergence;
volume of air required decreases as percentage of
submergence increases. An airlift is less efficient
when the volume of air injected exceeds the capac-
ity of the lift pipe. This condition can easily be
detected by a gurgling sound of air escaping from the
airlift. The water should emerge in a smooth even
stream; if it spurts, the cause is that either the air
volume injected is too great or the percentage of
submergence is too small.
The use of supplemental aeration can improve
water quality and fish production and decrease losses

Water discharge

Water level

Air inlet

Figure 6. Operating principles of an airlift.

Table 1. Approximate Pumping Rate for Airlifts of
Various Diameters and % Submergence.

Pipe sizes for Capacity at submergence (gal/min)
discharge pipe (in) 70% 60% 50%
1 13 10 9
1'4 20 14 12
11/2 28 22 16
2 50 40 30
3 110 100 75
4 260 200 160

in commercial fish ponds. However, the benefits for
a sportfish pond are not as clear-cut. Most instances
of oxygen depletion in sportfish ponds are the result
of a management error by the owner such as
overstocking, overfeeding, overfertilization, improper
chemical weed control, or pollution from barns and
feedlots. These management problems coupled with
hot cloudy weather and summer storms can cause ox-
ygen depletion. It is probably more economical for
the sportfish pond owner to adjust management
practices rather than to invest in supplemental

Carbon Dioxide
All waters contain some dissolved carbon dioxide.
Carbon dioxide (CO2) is an important compound for
the growth of plants and may also affect fish health.
Aquatic plants and phytoplankton remove CO2 from
the water during daylight hours as a part of
photosynthesis. Almost all living organisms add CO2
to the water continuously; at night when photosyn-
thesis stops, plants also add CO2. Thus, CO2 fluc-
tuates during a 24-hour period in a manner just the
opposite to that of dissolved oxygen.
Changes in CO, concentration cause the acidity (see
"Acidity") of the water to fluctuate during a 24-hour
period. When CO, is added to water, it forms an acid
resulting in a decline of the pH. Conversely, when
CO2 is removed, the pH of the water increases. The
presence of carbon dioxide can be a problem when
associated with oxygen depletion, but usually is not
a problem by itself. When dissolved oxygen is
limited, elevated CO, levels may interfere with the
ability of fish to take up the remaining oxygen. The
treatment of choice, mechanical aeration, not only in-
creases dissolved oxygen in the water, but also lowers
the level of carbon dioxide. The application of
hydrated lime at a rate of 30-50 lb/acre will reduce
the CO2 value in the water by precipitating as calcium
carbonate. About 1 ppm hydrated lime is needed to
neutralize 1 ppm CO,. In ponds with very low
alkalinities (see "Alkalinity and Hardness'), care
should be taken not to overtreat with hydrated lime,
which may cause pH to rise to toxic levels. Ponds
with chronically high CO2 concentrations frequently
have high total ammonia concentrations. Treatment
with hydrated lime will raise the pH and the result
is that a larger fraction of the total ammonia will be
in the toxic or un-ionized form, potentially endanger-
ing fish (see "Ammonia"). It should be noted that
treatment with hydrated lime does little to alleviate
the cause of high CO, levels; unless environmental
changes are made, CO2 levels may simply increase

The relationship between CO,, pH, temperature,
and alkalinity can be used to calculate CO2 concen-
trations. Table 2 can be used to determine CO2 levels
from the pH, temperature, and total alkalinity (ppm
CaCO,) of the water. Find the factor in the table that
corresponds to the observed pH and temperature,
and multiply this factor by the total alkalinity to find
the CO2 concentration; for example, at pH 7.4 and
68 F, alkalinity = 200 ppm as CaCO3. The factor
0.084 is taken from the table, so 0.084 X 200 = 16.8
ppm COz.
Generally, waters supporting good fish populations
have less than 5 ppm CO2. Carbon dioxide in excess
of 20 ppm may be harmful. If dissolved oxygen con-
tent drops to 3-5 ppm, lower CO, concentrations may
be harmful.

Dissolved nitrogen is not important as long as it
remains below 100% saturation. However, at super-
saturation levels even as low as 102%, it can cause
gas bubble disease in fish. Theoretically, gas bubble
disease can be caused by any supersaturated gas, but
in practice, the problem is almost always because of
excess nitrogen. Any reduction in gas pressure or in-
crease in temperature can bring nitrogen out of solu-
tion and form bubbles; the process is analogous to
the "bends" in scuba divers. These bubbles can lodge
in the blood vessels, restricting circulation, resulting
in death by asphyxiation. Gas supersaturation can
occur when air is drawn in by a high pressure water
pump or when air is injected into water under high
pressure that is subsequently reduced. Water that
is heated or drawn from deep wells is potentially
supersaturated. Water that has plunged over water-
falls or dams or is the result of snow melt may also
be supersaturated. However, these sources are of no
concern for Florida fish farmers.

Water inlet

Plastic filter

Large-mesh screen

Figure 7. Packed column for nitrogen supersaturation
and hydrogen sulfide.

Dissolved nitrogen can be reduced below super-
saturation by passing the water through a simple col-
umn made from a 10-inch-diameter pipe, 60 inches
long packed with plastic filter substrate. This device
can handle a flow rate of 100-150 gal/min (Figure 7).

Hydrogen Sulfide
Hydrogen sulfide (HS) is a serious problem in fish
farming. Incidents of H2S poisoning are far more

Table 2. Multiplication Factors to Determine Carbon Dioxide from pH, Temperature, and Total Alkalinity.*
410F 500F 590F 680F 770F 860F 950F
pH 50C 100C 150C 200C 250C 300C 350C
6.0 2.915 2.539 2.315 2.112 1.970 1.882 1.839
6.2 1.839 1.602 1.460 1.333 1.244 1.187 1.160
6.4 1.160 1.010 0.921 0.841 0.784 0.749 0.732
6.6 0.732 0.637 0.582 0.531 0.493 0.473 0.462
6.8 0.462 0.402 0.367 0.335 0.313 0.298 0.291
7.0 0.291 0.254 0.232 0.211 0.197 0.188 0.184
7.2 0.184 0.160 0.146 0.133 0.124 0.119 0.116
7.4 0.116 0.101 0.092 0.084 0.078 0.075 0.073
7.6 0.073 0.064 0.058 0.053 0.050 0.047 0.046
7.8 0.046 0.040 0.037 0.034 0.031 0.030 0.030
8.0 0.029 0.025 0.023 0.021 0.020 0.019 0.018
8.2 0.018 0.016 0.015 0.013 0.012 0.012 0.011
8.4 0.012 0.010 0.009 0.008 0.008 0.008 0.007
*For practical purposes, CO, concentrations are negligible above pH 8.4.


common than most fish farmers and biologists
realize. Hydrogen sulfide is a colorless, toxic gas with
an odor similar to rotten eggs. Hydrogen sulfide kills
fish by interfering with respiration. When fish are
first exposed, there is an increase in the killing rate;
later the killing rate slows, and finally respiration
Hydrogen sulfide is present in the water from wells
in certain locations and is present in ponds as a result
of bacterial decomposition of organic matter. Fish in
ponds are usually affected when crowded in a seine
during harvest. Stirring up the black odoriferous
sediments of the pond bottom during seining releases
H2S. Hydrogen sulfide is more toxic to fish at low
pH because a greater percentage of the HS is un-
ionized; raising the pH by liming can result in in-
creased survival of fish.
High temperatures greatly increase the toxicity of
H2S to fish. Fish at 50 F can tolerate five times as
much H2S as compared to tolerable levels at 68 F.
During summer months when water temperature
may exceed 90 F, a HS concentration that would be
harmless during winter can cause serious damage.
Well water containing H2S should be pumped
through an aeration device such as a half-open gate
valve or slotted cap to help volatilize the toxic gas
before it enters the pond. In raceways with acid water
and H2S, abundant aeration should be provided to
incoming water. It may help to have water flow over
a packed column of oyster shells (see Figure 7). Also,
the first segment of the raceway should be longer
than succeeding segments so that the gas can be
volatilized and so fish can detect and avoid the HS.
Fortunately, the effects of HS are reversible.
Potassium permanganate rapidly oxidizes hydrogen
sulfide. Therefore, if fish are suffering from H2S tox-
icity, the problem can be rapidly alleviated using 2-6
ppm potassium permanganate. If water pH is low,
the toxicity of HS can be reduced by the addition
of lime. When seining, bring the net in where there
is deep water and very little sediment. Potassium per-
manganate may be applied to the harvest area to ox-
idize the H2S if fish are to be held in the seine for an
extended period. Care must be taken in using
potassium permanganate because it too can be toxic
to fish at higher dosages.
Acidity refers to the capacity of the water to
donate hydrogen ions (H+). This includes the un-
ionized portion of weak acids such as carbonic acid
Sand tannic acid as well as salts like ferrous and/or
aluminum sulfate. The standard measure of acidity
is pH, the logarithm of the reciprocal of the hydrogen
ion concentration. The pH scale ranges from 1 to 14;

the lower the number, the greater the acidity. A pH
value of 7 is neutral. Fish are able to live in waters
within a pH range of about 3.5 to 10, but the
desirable range for most fish is generally considered
to be from 6.5 to 9.0. Many tropical fish species,
however, require acid waters for breeding and larval
development. Fish have less tolerance of pH ex-
tremes at higher temperatures. Ammonia toxicity
becomes an important consideration at high pH (see
"Ammonia"), and hydrogen sulfide is more toxic at
low pH.
The pH of pond water is influenced by the amount
of carbon dioxide present. Much of the CO2 present
is the result of animal and plant respiration. Carbon
dioxide is utilized during photosynthesis; therefore,
CO2 concentrations in water increase at night and
decrease during daylight hours. Since CO2 in water
is an acidic substance, the pH of water is usually
highest in the late afternoon and lowest just before
The amount of the daily pH fluctuation is
somewhat dependent upon the buffering capacity of
the water. Adding agricultural lime to a pond in-
creases the bicarbonate buffering capacity of the
water. This generally increases morning and lowers
afternoon pH values, thus lessening daily changes.
Accurate measurements of pond water pH are best
determined on site. The pH of water may change dur-
ing the interval between sampling and determination
in the laboratory. Various companies manufacture
field test kits and meters for measuring pH. For an
accurate measurement of daily changes in pH, pond
water should be sampled during early morning and,
late afternoon hours.
Alkalinity and Hardness
Alkalinity and hardness are similar but they repre-
sent different types of measurements. Alkalinity
refers to the capacity of the water to accept hydrogen
ions and is the direct counterpart of acidity. The
anions (negatively charged) or bases involved are
mainly carbonate (CO32-), bicarbonate (HCO,-), and
hydroxide (OH-); alkalinity refers to these in terms
of equivalent concentrations of calcium carbonate
(CaCO,). Originally, the hardness of any water was
the measure of the capacity of the water for
precipitating soap. Soap is precipitated chiefly by
calcium and magnesium ions, but may also be
precipitated by divalent ions of other metals, such
as aluminum, iron, manganese, strontium, and zinc,
and by hydrogen ions. When the hardness is
numerically greater than the sum of the carbonate
and bicarbonate alkalinities, the amount of hardness
which is equivalent to the total alkalinity is called
"carbonate hardness;" the amount of hardness in

excess of this is called "noncarbonate hardness."
Hardness, like alkalinity, is also expressed as CaCO,
equivalent concentration. Many authors incorrectly
use the term "hard water" to refer to water with high
alkalinity. Most waters of high alkalinity are hard
waters, but this is not always true. Fish culturists
often place undue emphasis on the total hardness of
water. Total hardness is usually not nearly as impor-
tant as total alkalinity in pond fish culture.
Fish grow over a wide range of alkalinity and hard-
ness. Natural waters that contain 40 mg/1 or more
total alkalinity are considered more productive than
waters of lower alkalinity. The greater productivity
does not result directly from alkalinity, but rather
from phosphorus and other nutrients that increase
along with total alkalinity. In fertilized fish ponds,
total alkalinity values in the range of 20-120 mg/1
have little effect on fish production. However, in fer-
tilized ponds containing less than 20 mg/1 total
alkalinity, fish production tends to increase with in-
creasing alkalinity. At low alkalinity, water may lose
much of its ability to buffer against changes in acid-
ity, and pH may fluctuate. Even when alkalinity is
zero, if weak acids such as tannic acid are present,
they may accept hydrogen ions, thereby buffering
changes in pH. Fish may also be more sensitive to
some toxic substances such as copper at low alkalin-
ity. Many tropical species, however, require low
alkalinity and soft water for survival of the eggs and
Determination of water hardness and alkalinity can
either be made on site with water test kits or by sub-
mitting a sample for analysis to a laboratory.
Agricultural dolomiticc) lime is recommended for in-
creasing alkalinity. Table 3 can be used as a guide
for liming; however, it is difficult to overtime a pond.

Table 3. Quantity of Dolomite Needed for Ponds of
Varying Alkalinity.
Total Alkalinity Dolomitic Lime/Surface Acre
12 ppm or less 1 ton
12-14 ppm 3/4 ton
15-25 ppm 14-12 ton
25 ppm or more None

Ammonia is excreted into the water by fish as a
result of protein metabolism. Some of the ammonia
reacts with water to produce ammonium ions, and
the remainder is present as un-ionized ammonia
(NH3). Un-ionized ammonia is much more toxic to fish
than ammonium. Standard analytical methods do not
distinguish between the two forms, and both are
lumped as total ammonia. The fraction of total am-

monia that is un-ionized ammonia (NH3) varies with
salinity, dissolved oxygen, and temperature, but is
determined primarily by the pH of the solution. For
example, an increase of one pH unit from 8.0 to 9.0
increases the amount of un-ionized ammonia approx-
imately 10-fold. These proportions have been
calculated for a range of temperatures and pH values
and are given in Table 4. Note that the amount of
NH3 increases as temperature and pH increase. To
calculate the un-ionized ammonia, determine the
percentage from the table by using the measured pH
and temperature values. Un-ionized ammonia (ppm)
= (ppm total ammonia X percentage of un-ionized
The amount of un-ionized ammonia that is
detrimental to fish varies with species. Growth rate
of trout declines and damage to gill, kidney, and liver
tissue is evident at 0.0125 ppm un-ionized ammonia.
Reduced growth and gill damage occur in channel
catfish exposed to levels greater than 0.12 ppm un-
ionized ammonia. Critical levels of un-ionized am-
monia have not been determined for many of
Florida's aquaculture species. Chronic exposure to
low levels of un-ionized ammonia may stress fish, in-
creasing the chance of infectious diseases.

Nitrite (NO2-), the intermediate product of the ox-
idation of ammonia to nitrate, is also toxic to fish.
Nitrite enters the blood of fish across the gill mem-
branes and combines with the oxygen-carrying por-
tion of red blood cells (hemoglobin) to form a com-
pound called methemoglobin which cannot carry oxy-
gen. Methemoglobin has a brown color, which it im-
parts to the blood of fish suffering from nitrite
poisoning, hence the name "brown blood disease."
Because nitrite interferes with oxygen uptake by the
blood, the symptoms of nitrite poisoning are quite
similar to those caused by oxygen depletion, except
that the symptoms persist throughout the day.
The nitrite concentration that is toxic to fish
depends on the species of fish, the amount of
chlorides (Cl-) present in the water, and the quan-
tity of dissolved oxygen. Rainbow trout are stressed
at 0.15'ppm nitrite and killed by 0.55 ppm. Channel
catfish are more resistant to nitrite, but 29 ppm can
kill them. Nitrites are usually not a problem if there
are three or more parts of chlorides present in the
water for every part of nitrite. Chlorides do not af-
fect the amount of nitrite in the water, but prevent
the uptake of nitrite by the blood of the fish. Any
time there is 0.1 ppm or more nitrites present, the
water should be checked for chlorides to see if salt
should be added. The addition of 25 ppm salt (NaC1)

Table 4. Percentage of Total Ammonia That
540F 620F
pH120C 160C
7.0 0.21 0.30
7.2 0.34 0.47
7.4 0.54 0.74
7.6 0.85 1.17
7.8 1.35 1.84
8.0 2.12 2.88
8.2 3.32 4.49
8.4 5.15 6.93
8.6 7.93 10.56
8.8 12.01 15.76
9.0 17.78 22.87
9.2 25.53 31.97
9.4 35.20 42.68
9.6 46.27 54.14
9.8 57.72 65.17
10.0 68.40 74.78
10.2 77.42 82.45

for each ppm nitrite has proven to be an effective
treatment. A freshwater flush is also recommended
to reduce nitrites.

Ammonia and Nitrite Removal
Biological removal is accomplished with cultures
of nitrifying bacteria that convert the ammonia first
to nitrite (NO2-) and then to harmless nitrate
(NO3-). These bacteria of genera Nitrosomonas and
Nitrobacter can be grown on almost any coarse
medium such as rocks, plastic, netting, or oyster
shells. Whole oyster shells are particularly well suited
because they contain calcium carbonate, which con-
tributes to the chemical reactions and buffers pH
changes. In addition, the size and shape of whole
oyster shells result in considerable surface area for
bacterial attachment and provide large void spaces
that resist clogging. The latter aspect is of great im-
portance because backflushing of a clogged filter also
removes a considerable amount of nitrifying bacteria,
which reduces the effectiveness of the filter. Filters
of this material have been used for fish culture for
many years at the University of Florida Research
Water should be pretreated before it reaches the
filter bed to insure adequate oxygen for bacteria and
to reduce the load of particulate matter that could
clog the filter. Aeration in the fish tank followed by
a settling tank or clarifier is recommended for this
purpose. In addition to providing oxygen, aeration
also causes the formation of particulate aggregates
that are easily removed by sedimentation. Panels of
nylon netting have been shown to increase the effec-
tiveness of settling tanks by reducing water current

Is Un-ionized at Varying pH and Temperature.
680F 750F 820F
200C 240C 280C
0.40 0.52 0.70
0.63 0.82 1.10
0.99 1.30 1.73
1.56 2.05 2.72
2.45 3.21 4.24
3.83 4.99 6.55
5.94 7.68 10.00
9.09 11.65 14.98
13.68 17.28 21.83
20.08 24.88 30.68
28.47 34.42 41.23
38.69 45.41 52.65
50.00 56.86 63.79
61.31 67.63 73.63
71.53 76.81 81.57
79.92 84.00 87.52
86.32 89.27 91.75

and also provide additional surface for nitrifying
bacteria. Several designs of nylon netting-oyster shell
filters are illustrated in Figure 8.
Sponge filters have been shown to be effective for
biological filtration of water in aquariums and vats.
Sponge filtration has generally been accepted as a
strictly mechanical process. However, if the sponge
is cleaned by a gentle squeeze rather than a vigorous
wash, it will develop a bacterial population that will
effectively neutralize ammonia. Sponge filters are
especially useful during fry rearing. The size of com-
mercially available sponge filters is limited and the
cost is somewhat high. Sponge filters, however, are
extremely easy to make. Several designs are depicted
in Figure 9. Sponge may also be used to replace the
filter media in undergravel and external power filters
for aquaria.
Aquatic plants in marshlands have inadvertently
served as natural waste treatment systems for cen-
turies. However, only in more recent years have
researchers found that wastewater can be improved
by passing it through wetland areas. Emergent
plants such as cattails (Typha), reeds (Phragmites),
and bulrushes (Scripus) have been utilized in artificial
marshes for wastewater treatment. Waterhyacinths
(Eichhornia crassipes) are also valuable for this pur-
pose. A two-pond system using waterhyacinths in the
first and cattails in the second pond has been recondi-
tioning water for fish culture at the University of
Florida Research Laboratory for many years. The
system is low-cost, reliable, and low-maintenance.
The aquatic plants not only provide surface area for
attachment of nitrifying bacteria, but also take up
nutrients directly from the water for growth. Aquatic





Recirculation water



Fresh water-

Air supply -


IIJ Pump


Figure 8. Designs of nylon netting-oyster shell biological filters.

Fresh water

Air supply



Fresh water

Air supply

Drain -



Metal conduit for
cutting sponge

Edge sharpened with file
and serations cut with

Silicone cement

Plexiglas or aluminum
plate glued to sponge
with silicone cement

Figure 9. Designs of sponge biological filters.


Lead weigh

Lead weight

plants can also be used in tanks or aquaria for
biological filtration. Several aquatic plant filter
designs are illustrated in Figure 10.
Establishing a bacteria population in a biological
filter is a slow process during which water quality
undergoes several changes. Two weeks to three
months may be required for the filter to stabilize. In
the initial stage, high ammonia levels predominate
until nitrifying bacteria become established. There
is also a time lag between the fall of ammonia levels
and the oxidation of nitrite, because the growth of
Nitrobacter is inhibited by the presence of ammonia.
Efficient oxidation of nitrite to nitrate does not take
place until most of the ammonia has been converted
by Nitrosomonas.
Water should be circulated through the filters for
several weeks before the fish or invertebrates are
added to the system. During this period ammonium
chloride (NH4CI) in solution with water may be added

by gradual drip over an 8-hour period daily at a level
of 0.02-0.03 mg/1 NH, (calculated) in the entire
system. The NHC1 should be added to the inlet side
of the biofilter. The daily addition of NH,C1 is
analogous to addition of waste material by the fish
once the system is stocked and stimulates the
development of the nitrifying bacteria without sub-
jecting the fish to the high ammonia levels associated
with the start-up period of a biofilter.
Adding specimens a few at a time is always a good
technique with a new filter system. If the species to
be cultured are sensitive to ammonia and nitrite
poisoning, the animal load should be gradually built
up to maximum density.
Seeding a new system with substrate from an
established biological filter is the only reliable
method to accelerate the conditioning process. Part
of the detritus should be included, since it contains
substantial numbers of bacteria.

Figure 10. Designs of aquatic plant biological filters.

Recirculatlon water
to fish tanks



Recirculation water
to fish tanks

Drain water from Waterhyacinths
fish tanks

Physical Factors

Temperature has a direct effect on fish metabolism,
feeding, and survival. No other physical factor affects
the development and growth of fish as much as water
temperature. Metabolic rates of fish increase rapidly
as temperature goes up. Conversely, as temperature
decreases, so does the fish's demand for oxygen and
food. Many biological processes such as spawning
and egg hatching are geared to annual changes in
environmental temperature. Each species of fish has
a temperature range that it can tolerate; within that
range, there is an optimum temperature for growth
and reproduction, which may change as the fish
grows. Like fish, disease organisms also have an op-
timum temperature range for development, and out-
breaks are more prevalent during these conditions.
Most chemical substances dissolve more readily as
temperature increases; in contrast, gases such as
oxygen, nitrogen, and carbon dioxide become less
soluble as temperature rises.
Large, rapid changes in temperatures are stressful
to fish and may result in death. This problem is most
important when fish are transported for stocking.
Prior to stocking, water in the transport container
should be tempered with the water in which the fish
will be stocked. For small sensitive fry, a tempering
rate of 3.60F/hr is suggested. Larger more hardy fish
can withstand more than a 9F/hr change in
temperature. Tropical fish species can generally
tolerate an increase in water temperature better than
a decrease. The opposite is true for temperate and
cool-water species. Fish that initially survive a
temperature shock may be sufficiently stressed to
later succumb to infection.
Temperature has an indirect effect on the fish as
a result of water stratification. As temperature
changes, so does water density. The temperature at
which water is at its maximum density is 39.2F. In
early spring, pond water temperature is uniform from
surface to bottom. As the days become warmer, the
surface water becomes warmer and lighter. By early
summer, the pond may become stratified into three
layers: the upper oxygen-rich, warmer layer called the
epilimnion; the transition layer or thermocline, which
is characterized by a rapid change in temperature;
and the lower, oxygen-poor, cooler layer called the
hypolimnion. The density difference of the water in
these layers resists mixing. In temperate regions, the
differences in temperature between these layers may
become quite pronounced. The subtropical waters of
Florida, however, can stratify with very little dif-
ference in temperature. This is because of the greater
change in water density at higher temperature; a 1F

increase in temperature at 900F results in 3.4 times
the change in water density as a similar temperature
increase at 500F. As a result, temperature differences
between layers are not as distinct, even though the
body of water is stratified. Temporary stratification
and turnover may occur many times during the sum-
mer as a result of strong winds and rains.
Turnover can cause water quality problems
because the lower layer of water usually contains
decaying organic matter, little oxygen, and toxic
products of decomposition. The signs of summer
turnover are a rapid change in water color to a brown,
black, or gray, a putrid odor, and fish gulping at the
surface. These symptoms are usually observed after
periods of heavy wind and rain. Turnover may also
occur with the loss of a phytoplankton bloom
resulting in increased sunlight penetration, warming
the water to greater depth.
In small ponds and lakes, stratification can be
prevented by routine use of mechanical aerators to
maintain constant mixing (see "Dissolved Oxygen").
This procedure results in more constant dissolved
oxygen concentration at all levels and helps to pre-
vent the succession of algae from the desirable greens
to undesirable blue-greens.
Many tropical fish species cannot withstand the
winter temperatures prevalent in Florida. As a result,
ponds must be covered with plastic greenhouses to
increase water temperature. Most tropical fish farms
utilize cross-supports of wood or pipe to hold up the
plastic pond cover. The University of Florida uses
a low-cost inflatable greenhouse that does not require
cross-supports over the pond. The plastic is held up
by air pressure provided by a small (0.04 HP) squirrel
cage blower. The plastic sheet is secured at the edges
by a simple wooden interlocking frame that sur-
rounds the perimeter of the pond. The frame allows
attachment of the plastic without puncturing (Figure
11). A commercially available aluminum interlocking
frame can also be used to attach the plastic, but it
is more expensive. During extreme cold weather,
when ice was forming over the surface of uncovered
ponds at the research facility in Gainesville, water
temperature in ponds covered with inflatable
greenhouses did not drop below 580F. Water in fish
tanks can be warmed by solar hot water heaters, elec-
tric immersion heaters, gas fired boilers, or well water
flush. Tanks should be protected by a heated
greenhouse or insulated building.

Turbidity refers to the amount of suspended solids
in the water, which hinders light penetration. Turbid-
ity can be the result of planktonic algae (green water)

Figure 11. Inflatable greenhouse with wooden interlocking frame.

or clay particles in suspension. Humic acids in ponds
impart a weak tea or coffee color to the water, which
also hinders light penetration; for many tropical
species of fish, this water is valuable for spawning
and maximum coloration. Although turbidity and
color do not usually affect the fish directly, clay
turbidity and humic stain limit light penetration and
may result in less productive waters. Planktonic
algae, however, are desirable because these micro-
scopic plants provide the basis for the food chain for
the entire pond, resulting in increased fish production.
Most clay turbidity problems are the result of
exposed soil in the watershed, crayfish, bottom-
feeding fish such as carp and catfish, or livestock
wading in the pond. Newly constructed ponds may
also have clay turbidity problems. Ponds which
remain turbid for long periods of time should be
treated. The following treatments are only tempo-
rary. Therefore, the source of clay turbidity should
be eliminated prior to treatment. Before using one
of these treatments, be sure that the turbidity is
caused by clay suspension and not phytoplankton,
which can look quite similar. Microscopic examina-
tion is required to distinguish clay turbidity from
planktonic algae.
Clay Turbidity
* 80 lb/acre-foot (see "Determination of Pond
Dimensions for Treatment") of commercial alum.
To avoid pH reduction and possible fish kill,
simultaneously apply 30 lb/acre-foot of hydrated
300-500 lb/surface acre of gypsum (land plaster).
7-10 bales of hay and 40 lb superphosphate/sur-
face acre.

* 100 lb/surface acre cottonseed meal spread over
entire surface. Avoid last two treatments during
the summer because oxygen depletion may result.
Humic Acid Color
* Apply 1 ton/surface acre of agricultural lime.

Adding fertilizer to pond waters stimulates the
growth of phytoplankton (green water) and small
aquatic invertebrates (zooplankton and insects) that
feed on the phytoplankton, thus improving the
growth of fish that feed on the invertebrates. Before
recreational ponds and lakes are fertilized, a fishery
biologist should be consulted.
Fertilization of production ponds is complex and
rates vary among locations and from pond to pond.
Before starting a fertilization program, the water
should be tested for nutrients, similar to a soil test
before planting a crop. The objective is to maintain
a phytoplankton bloom of a density that allows the
pond owner to observe a light-colored object at a
depth of approximately 18 inches. This can be deter-
mined by attaching a pie plate to a yardstick, or more
simply by extending your arm down into the water;
you should be able to see your hand down to slightly
over elbow depth. You may need to add fertilizer
every week or two to maintain the bloom. Liquid
fertilizer (ammonium polyphosphate) may be more
efficient for pond fertilization than granular forms.
Rates of fertilization should start at 11/2-2 gal/acre-
foot and then be adjusted for your particular
To prevent undesirable blue-green algal blooms,
nitrogen should be added every time phosphorus is

used. By using liquid fertilizer, this is accomplished
automatically. Blue-green algae may also be
prevented by adding organic material such as hay,
manure, and cottonseed meal with the inorganic fer-
tilizer. This treatment should not be used during hot
weather because of the risk of oxygen depletion.

Pond Renovation
Ponds containing undesirable fish species such as
gar, bowfin, carp, bullheads, or stunted sportfish
populations should be renovated. Renovation is also
desirable when the crop of fish has been harvested.
The ponds simplest to renovate are those equipped
with a drainpipe. These ponds should be dried, limed
if necessary, and disked prior to refilling. In Florida,
many ponds cannot be drained due to the high water
table and topography. For small ponds, gasoline-
powered pumps can be used. Hydrated lime (1 ton/
acre) should be spread evenly over the bottom before
refilling. For ponds too large to be drained, rotenone
is the treatment of choice.
Rotenone in liquid or powder form is effective for
pond renovation. Use 1 gal of liquid (5% active) or
10 lb of powder (5% active) rotenone per acre-foot of
water. Rotenone kills fish and invertebrates by
inhibiting oxygen transport across the gills (suffoca-
tion). Rotenone dissipates quickly in water; the
residue usually disappears within two weeks.

Rotenone is most effective at water temperatures
above 700F so apply during warm months. Dilute the
liquid rotenone at a 1:5 ratio with water. Mix powder
form with enough water to make a slurry, and then
dilute at a 1:5 ratio with additional water. Distribute
the rotenone evenly over the entire pond and
throughout the water column to avoid leaving refuge
areas for fish to escape. Shallow water and heavily
vegetated areas require particular attention. The
effectiveness of rotenone depends on fish species;
shad, sunfish, shiners, carp, and bass are sensitive,
but bullhead catfish, tilapia and gar can be difficult
to kill.

Determining Pond
Dimensions for Treatment
To determine the proper amount of chemical
necessary for treatment, an estimate of the volume
in acre-feet is required. To estimate the water volume,
first determine the average depth in feet by measur-
ing with a weighted line or calibrated pole. Take
measurements every 10 to 20 feet along the long and
short axis of the pond (Figure 12). Second, determine
the surface area of the pond in acres. Measure the
entire shoreline to determine the area of a round
pond; measure length and width for a rectangular
pond, and determine base and height for a triangular
pond (Figure 13). Multiply the average depth and
surface area to determine water volume in acre-feet.

O0' 0'
,1' 3'
2' 6'
4' 0' 3' 8' 4' 0'
6' 5'
0' 2' 4' 5' 6' 5' 3' 2' O' 3' 5' 4' 0'
3' 6' 8' 5' 4' O' \ 3'
4' 0
3' 3'
2' 2'
0' 0'

Number of
readings 17 16 11

Total readings 49 48 32

Average depth 49 17 = 2.9 ft 48 16 = 3 ft 32 11 = 2.9 ft

Figure 12. Determining average depth of ponds (in ft).

250 ft.

shoreline shoreline average
length length depth
(250 x 250 x 2.9)/547,390 = 0.33 acre-ft

length x width x depth
(400 x 200 x 3)/43,560 = 5.5 acre-ft

400 ft. 400 ft.
length heigth

'/2(base) x height x depth

('/2(200) x 400 x 2.9)/43,560 = 2.7 acre-ft

Figure 13. Determining pond water volume (in acre-ft).

In conclusion, it is important to remember that
water quality does not remain constant and therefore
must be monitored frequently.
The various factors of water quality are inter-
related. A change in pH can affect the toxicity of
ammonia, hydrogen sulfide, and carbon dioxide.
Hydrogen sulfide and carbon dioxide are more of a
problem when dissolved oxygen is low. Changes in
temperature affect the toxicity of ammonia and
hydrogen sulfide, the amount of dissolved oxygen
present, and the potential of nitrogen supersatura-


Useful Tables and Conversions

Conversion Factors
1 liter of water
= 1 kilogram
= 2.205 pounds
1 milliliter or cubic centimeter of water
= 1 gram
= 0.0353 ounce

1 gallon of water
= 8.34 pounds
= 3.785 kilograms
1 cubic foot of water
= 62.36 pounds
= 28.29 kilograms
1 fluid ounce
= 1.043 ounces
= 29.57 grams
1 acre
= 43,560 square feet
= 208.7 x 208.7 feet
= circle diameter 235.5 feet
1 acre-foot
= 1 surface acre 1 foot deep
= 43,560 cubic feet
= 2,718,144 pounds
= 1233.49 cubic meters
= 325,851 gallons
1 cubic foot per second
= 448.83 gallons per minute
= 26,930 gallons per hour
= 646,320 gallons per day
= 1.699 cubic meters per minute
= 101.93 cubic meters per hour
= 2446 cubic meters per day

1 part per million (ppm)
= 1226 grams per acre foot
= 0.0283 gram per cubic foot
= 2.7 pounds per acre foot
= 0.0038 gram per gallon
= 0.0000623 pound per cubic foot
1 percent solution
= 38 grams per gallon
= 1.3 ounces per gallon
= 0.622 pound per cubic foot of water

pi = 3.1416
Area of a circle = pi x radius2
Area of a triangle = (base x height)/2
General dilution formula:
(desired concentration x desired volume)/(concentration of stock solution)
= volume of stock solution to be diluted to desired volume

Pounds to Add to Obtain Desired Concentration
Acre Feet
ppm 1 2 3 4 5 6 7 8 9 10
0.1 0.27 0.54 0.81 1.08 1.35 1.62 1.89 2.16 2.43 2.70
0.3 0.81 1.62 2.43 3.24 4.05 4.86 5.67 6.48 7.29 8.10
0.5 1.35 2.70 4.05 5.40 6.75 8.10 9.45 10.80 12.15 13.50
1.0 2.70 5.40 8.10 10.80 13.50 16.20 18.90 21.60 24.30 27.00
2.0 5.40 10.80 16.20 21.60 27.00 32.40 37.80 43.20 48.60 54.00
3.0 8.10 16.20 24.30 32.40 40.50 48.60 56.70 64.80 72.90 81.00
4.0 10.80 21.60 32.40 43.20 54.00 64.80 75.60 86.40 97.20 108.00
5.0 13.50 27.00 40.50 54.00 67.50 81.00 94.50 108.00 121.50 135.00
10.0 27.00 54.00 81.00 108.00 135.00 162.00 189.00 216.00 243.00 270.00
15.0 40.50 81.00 121.50 162.00 202.50 243.00 283.50 324.00 364.50 405.00
20.0 54.00 108.00 162.00 216.00 270.00 324.00 378.00 432.00 486.00 540.00
25.0 67.50 135.00 202.50 270.00 337.50 405.00 472.50 540.00 607.50 675.00

Grams to Add to Obtain Desired Concentration*
Cubic Feet
ppm 10 50 100 200 300 400 500 1000 2000 3000
0.5 0.14 0.7 1.4 2.8 4.2 5.7 7.1 14.2 28.3 42.5
1 0.28 1.4 2.8 5.7 8.5 11.3 14.2 28.3 56.6 84.9
2 0.57 2.8 5.7 11.3 17.0 22.6 28.3 56.6 113.2 169.8
3 0.85 4.2 8.5 17.0 25.5 34.0 42.5 84.9 169.8 254.7
4 1.1 5.7 11.3 22.6 34.0 45.3 56.6 113.2 226.4 339.6
5 1.4 7.1 14.2 28.3 42.5 56.6 70.8 141.5 283.0 424.5
10 2.8 14.2 28.3 56.6 84.9 113.2 141.5 283.0 566.0 849.0
15 4.2 21.2 42.5 84.9 127.4 169.8 212.3 424.5 849.0 1273.5
20 5.7 28.3 56.6 113.2 169.8 226.4 283.0 566.0 1132.0 1698.0
25 7.1 35.4 70.8 141.5 212.3 283.0 353.8 707.5 1415.0 2122.5
*0.0283 gram in 1 cubic foot of water gives 1.0 ppm; 0.0038 gram in 1 gallon of water gives 1.0 ppm.

Conversion of Volume Units

Unit Gallon Quart PintCubic Milliliter Liter Cubic
Unit Gallon Quart Pint Ounce Foot Inch Meter

Gallon 1 4 8 128 0.1337 231.0 3,785.4 3.785 0.00378
Quart 0.25 1 2 32 0.0334 57.75 946.36 0.946 0.00095
Pint 0.125 0.5 1 16 0.0167 28.88 473.18 0.473 0.00047
Fluid ounce 0.0078 0.0313 0.0625 1 0.00104 1.805 29.573 0.0296 0.00003
Cubic foot 7.481 29.92 59.84 957.5 1 1,728 28,317 28.32 0.02832
Cubic inch 0.0043 0.0173 0.0346 0.5541 0.00058 1 16.39 0.0164 0.000016
Milliliter 0.00026 0.00106 0.0021 0.0338 0.000035 0.060 1 0.001 0.000001
Liter 0.2642 1.057 2.1134 33.81 0.0353 61.02 1,000 1 0.001
Cubic meter 364.2 1,057 2,113 33,810 35.3 61,000 1,000,000 1,000 1

Conversion of Length Units
Unit Inch Foot Yard Millimeter Centimeter Meter
Inch 1 0.0833 0.0278 25.40 2.540 0.0254
Foot 12 1 0.3333 304.8 30.48 0.3048
Yard 36 3 1 914.4 91.44 0.9144
Millimeter 0.0394 0.0033 0.0011 1 0.1 0.001
Centimeter 0.3937 0.0328 0.0109 10 1 0.01
Meter 39.37 3.281 1.0936 1,000 100 1

Conversion of Weight Units
Unit Grain Ounce Pound Milligram Gram Kilogram
Grain 1 0.0023 0.000143 64.8 0.0648 0.000065
Ounce 437.5 1 0.0625 28,350 28.35 0.0284
Pound 7,000 16 1 453,590 453.6 0.4536
Milligram 0.0154 0.00035 0.000002 1 0.001 0.000001
Gram 15.43 0.0353 0.0022 1,000 1 0.001
Kilogram 15,430 35.27 2.205 1,000,000 1,000 1

This publication was produced at a cost of $1,073.00, or 54 cents per copy, to inform pond owners about
water quality maintenance to protect fish health. 6-2M-88 *

director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and
June 30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institu-
tions that function without regard to race, color, sex or national origin. Single copies of Extension publications (excluding 4-H and Youth publica-
tions) are available free to Florida residents from County Extension Offices. Information on bulk rates or copies for out-of-state purchasers is ""..
available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this publication,
editors should contact this address to determine availability.