WATER QUALITY
What You Need To Know
To Keep Your Fish Alive
Gary Fornshell, University of Idaho
Terry Patterson, College of Southern Idaho
To a great extent, the
success or failure of
fish culture is
determined by water
quality
Water Quality – Why Is It Important?
• Your fish live in it
• Are supported by it
• Receive their oxygen from it
• And excrete in it
Water Quality – Why Is It Important?
• Water quality factors influence and interact
with each other
• What may cause problems in one situation
may be harmless in another
• Influences effectiveness/toxicity of
treatments
Water Quality – Why Is It Important?
• Most disease problems can be avoided
with proper management of water
quality
• This includes maintaining water quality at a
level that provides an environment
conducive to fish health and growth
Water Quality Variables
• Temperature
• Dissolved oxygen
• Total ammonia-nitrogen, NH3, NO-2
• Alkalinity
• Hardness
• pH
• Carbon dioxide
Water Quality Variables
Temperature
• For each 10°C (18°F) rise in
temperature the metabolic rate doubles
• Controls the reaction rate of chemicals
• Influences solubility of gases in water
• Influences toxicity of ammonia and therapeutants
• Optimum temperature for tilapia growth is 85-88 °F
Water Quality Variables Dissolved
Oxygen
• First limiting factor for growth and fish health
• Solubility decreases with increasing
temperature and elevation
• Respiratory rate increases with increasing
temperature, activity and feeding
• In general the minimum DO should be ≥ 60%
of saturation or ≥ 5 ppm (mg/L)
• > 2 ppm in biofilter effluent
Water Quality Variables
Total Ammonia-Nitrogen
• Usually the second limiting factor – nitrogenous
waste: feces & feed
•TAN includes ammonium ion (NH4+)
and ammonia (NH3)
• The proportion of NH3 increases with increasing
temperature and pH
• < 0.05 mg/L NH3
• < 0.5 mg/L nitrite-N (NO-2)
,
Percent of Total Ammonia
in the Un-Ionized Form at
Various Temperatures and pH
percent Ammonia
Temperature (ºF)
(pH) 7.0
8.0
9.0
___________________________________________
50º
0.19
1.83 15.7
68º
0.40
3.82
28.4
86º
0.80
7.46
44.6
The Nitrogen Cycle
Water plants
Food
Excess
food
Algae
Nitrate (NO 3 )
Fishes
Urine
Feces
Urea
Nitrite (NO 2 )
Ammonia
(NH 3 )
Peptides
Amino acids
Time Required
for Bio-Filter to Mature
0.8
8
NO 3
0.6
Ammonia
(mg/l)
NH 3
NO2
6
0.4
4
0.2
2
0.0
0
2
6
10
14
18
Time in Days
22
Nitrites &
Nitrates
(mg/l)
Water Quality Variables - Alkalinity
• Is the buffering capacity of water –
absorbs acids and/or bases
• High alkalinity prevents wide pH fluctuations
• Maintain levels between 75-120 mg/L as CaCO3
• 7 grams of alkalinity consumed by 1 gram of NH3
Effects of pH on Various Buffers
Percent of Total CO 2
100
-
Free CO 2
=
HCO3
CO 3
50
0
4
5
6
7
8
pH
9
10
11
12
Water Quality Variables
• Hardness
50 – 100 mg/L as CaCO3
• pH
7–8
• Carbon dioxide
< 20 mg/L
Water Quality Variables
Total Dissolved Gases
Supersaturation caused by:
• leaking water lines
• air leak on low pressure side of pump
• source of water
• mixing cold and hot water
Recommended total dissolved gas pressure <104%
Water Balance in Freshwater Fish
Water
Salts
Ammonia
Large quantities
of dilute urine
Stressors
• Poor water quality
• Environmental conditions
• Improper handling
Most Fish Diseases
Are Stressed Mediated
Stress is a physiologic state caused by a procedure,
environmental condition or other factor which interferes with
the fish’s ability to maintain a “normal” state. It extends the
adaptive responses of an animal beyond the normal range or
which disturbs the normal functioning.
Low Level Mortality
100%
Peracute
M
O
Acute
R
T
A
L
Chronic
I
T
Y
0%
Time
Usually the first sign of water
quality/environmental
problems
Loading Effects
Number of fish which can
successfully live and grow
in a given amount of water
depends on:
• DO level
• Metabolic rate of the
fish
• Amount being fed
• Pathogen load
• Water exchange rate
Management Recommendations
• Maintain water quality within suggested guidelines
• Maintain fish loadings at optimum levels of 1/4 to
1/3 lb./gallon (1/2 lb./gallon maximum)
• Monitor water quality on a regular basis/keep good
records
Management Recommendations
• Low DO: increase aeration; stop feeding
• High CO2: increase aeration; add air stripping
column
• Low pH: add sodium bicarbonate; reduce feeding
rate; check ammonia & nitrite
• High NH3: exchange system water; reduce feeding
rate; check biofilter, pH, alkalinity & DO
in biofilter
• High nitrite: exchange water; reduce feed; add 6
ppm chloride per 1 ppm nitrite; check
biofilter, pH, alkalinity & DO in biofilter
Good Stuff To Know
• ~ 300 square feet biofilter material per 100 lbs. fish
• Add 0.125 to 0.167 lbs. baking soda/ 100 gallons to
maintain alkalinity
• Add 0.275 to 0.413 lbs salt/100 gallons to maintain
chloride levels of 200 – 300 ppm
• Do not make any rapid changes to any WQ
parameter, except to increase DO
Resources
• SRAC Publications:
http://www.msstate.edu/dept/srac/publicat.htm
• Hach WQ test kits: http://www.hach.com/
• LaMotte WQ test kits: http://www.lamotte.com/
• Equipment Suppliers:
• http://aquaticeco.com/
• http://www.tecinfo.com/~aqcenter/
• Eagar, Inc. 1-800-423-6249